1
Q
How does the epithelium differ between these 2 pictures
A
Presence of pericyte in A. These cells are crucial for the function of the blood-brain barrier (controls molecular transport between blood & CNS
2
Q
Label the structures
A
3
Q
Label the numbers and circles
A
4
Q
Are there any pathological findings in this MRI of dogs head
A
pituitary mass at D
5
Q
Label the structures
A
6
Q
What are the types of cell communication
A
Autocrine
- Affects cell producing them e.g., growth factors
Paracrine
- Diffuse short distance to affect cells nearby e.g., neurotransmitters
Endocrine
- Acts on target cells distance from site of synthesis - hormones
7
Q
compare lipid soluble to water soluble hormones
A
Lipid soluble
- Transported in blood by carrier proteins
- Diffuse through plasma membrane
- Alters expression of genes at level of nucleus
- e.g. steroid hormones, thyroid hormones, vit D
Water soluble
- Easily travel in blood
- Bind to receptors on surface of cell
- Results in series of intracellular events
- most signalling molecules
8
Q
Where does the pineal gland develop from
A
From CNS
9
Q
Where does the thyroid gland develop from
A
From floor of mouth
10
Q
Where does the parathyroid gland develop from
A
From pharyngeal arches
11
Q
Where does the adrenal gland develop from
A
Medulla from neuroectoderm
Cortex from mesoderm (mesonephros)
12
Q
What is the function of nuclear receptors
A
13
Q
What are the 3 components of membrane receptors
A
External domain (binds signal)
Transmembrane domain
Cytoplasmic/intracellular domain
- undergoes conformational change which activates signalling pathway
14
Q
What is the function of growth factors and cytokines
A
Control fundamental processes
- Cell division (ie cell proliferation)
- Cell differentiation
- Programmed cell death (apoptosis)
Aberrant function of growth factors & cytokines are therefore implicated in cancer
15
Q
Describe some pathways of growth factors
A
Growth factor receptors have enzyme activity (specifically tyrosine kinase)
Ligand binding activates this enzyme & initiates signal that is propogated through cell by phosphorylation
Can occur in many ways (main one through small nucleotide binding protein Ras)
Other ways involve phospholipase C or phosphitidyl-inosital 3 kinase
Ultimately activates transcription factors & hence production of growth response genes
16
Q
What is half-life
A
Time taken for concentration of signalling molecule to fall by half
Transient signals may have long lasting effects
Many intracellular proteins have short half lives - determined by:
- Rate of synthesis
- Modifications of proteins e.g., + and - phosphate groups
17
Q
What are the main classes of cell surface receptors
A
Ion-channel-linked receptors
- Rapid synaptic signalling
G-Protein linked receptor
- Act indirectly to activate separate plasma membrane bound protein
Tyrosine kinase-linked receptor
- Directly associated with enzyme they activate
Receptors with intrinsic enzymatic activity
- Functions directly as enzyme
18
Q
Describe ion channel linked receptors
A
- Signal molecule (neurotransmitter) binds to receptor
- This opens (or closes) ion channel
- Ions move into cell passively by diffusion
- Excitability of post-synaptic cell altered
Examples of ion-channel-linked receptors:
- post-synaptic membranes
- Neuromuscular junction
- Nicotinic acetylcholine receptor
- GABA receptors
19
Q
Describe G protein linked receptors
A
Receptor-protein interaction is mediated by a 3rd protein
- This is the G protein
The target protein may be an enzyme or ion channel
e.g. muscarinic acetylcholine receptor
20
Q
What are second messengers
A
Second messengers are small intracellular signalling molecules
Generated in large numbers by receptor activation: Amplification of signal
Rapidly diffuse away
Pass signal on by binding to & altering behaviour of other proteins
Exhibit different ways of passing signal on
21
Q
Describe classical hormones
A
Secreted from endocrine cells
Diffuse into blood
Transported by transporters via blood to target tissue
Example: Cortisol
22
Q
Describe neurohormones
A
Synthesized within neuroendocrine cells
Secreted from nerve terminals
Diffuse into blood vessels and transported
Eg: Corticotropin-releasing hormone (CRH)
23
Q
Describe water vs lipid soluble hormones & give examples
A
Water-soluble hormones
- Example: Catecholamines (epinephrine)
- Freely transported
Lipid-soluble hormones
- Examples: Cortisol and thyroid hormones
- Bound to transport proteins
- (cortisol-binding globulin [CBG])
24
Q
What are free hormones
A
active
25
What are the functions of transport proteins
Serve as a hormone reservoir
Act as hormone buffers
Reduce hormone loss via the kidneys
26
How can hormones be eliminated
Enzymatic degradation
Within target cells after binding receptor
Via liver and kidneys
27
How are fast action hormones (e.g. epinephrine) eliminated
Fight and Flight hormone
Rapid release from the adrenal medulla
Immediate action on tissues (heart)
Fast return to normal (few seconds)
Water-soluble hormone binds receptors
Enzymatically degraded within cell
28
How are slow action hormones (e.g. T4) eliminated
Circulates as bound (99.7%) or free (0.03%) hormone (lipid-soluble)
Bound hormone resistant to degradation
Either converted into T3, which enters cells & alters gene expression
Or converted into water-soluble compounds by liver & excreted in urine
29
What factors affect hormone responses
Variation by tissue
Variation by time
- age, species
Variation by dose
Status of target tissue
30
Describe how hormone response is affected by tissue variation (use thyroxine as example)
Tissues respond differently to the same hormone
Example: Thyroxine
Increases cellular metabolism
Measured as oxygen consumption
When measured 48 hours after injection
Most stimulated tissues: Heart, gastric mucosa
Least stimulated tissues : Skeletal muscle
Not stimulated tissues : Spleen and brain
31
Describe how hormone response is affected by status of target tissue
With overstimulation, target tissues hypertrophy
- More functional tissue
- Leads to exaggerated responses
With understimulation, target tissues atrophy
- Less functional tissue
- Inadequate responses
32
What are negative feedback loops in endocrinology
Negative feedback regulation
- If hormone level exceeding need
- High level sensed by hypothalamus &/or pituitary gland
- Hormone synthesis decreases
It is the free hormone that is monitored
Adapt to changes in binding protein
33
What are the 9 endocrine glands
34
What are the regions of the pituitary gland
anterior pituitary = adenohyphysis/pars distalis
Posterior pituitary = neurohyphysis/pars nervosa
35
Where does the pituitary gland develop from
adenohypophysis/anterior = ectoderm from roof of mouth (Rathke’s pouch)
neurohypophysis/posterior = downgrowth of ectoderm of forebrain
36
What is the embryological origin of the brain
Neural folds move together and fuse => neural tube
Neural tube gives rise to tissues of CNS - brain and spinal cord
37
What is the cause of pituitary dwarfism
Rathke’s pouch doesn’t differentiate into glandular tissue of adenohypophysis (anterior pituitary) => no growth hormone
38
What is the infundibulum of the pituitary gland
connection between brain and neurohypophysis/posterior pit.
39
Label the brain
40
Describe the sections and functions of the adenohypophysis/anterior pit.
Pars tuberalis – monitors melatonin levels
Pars intermedia – Rathke’s pouch remnant. Produces melanocyte stimulating hormone in foetus
Pars distalis – main secretory region. Collection of cells, each secrete different hormone
41
Describe the sections of the neurohypophysis/posterior pit
42
Give examples of water soluble hormones
insulin, adrenaline, noradrenaline, glucagon, cortisol, FSH, LH, ADH
43
Which hormones exclusively use the adenyl cyclase pathway
ACTH
calcitonin
44
Which hormones exclusively use the phospholipase C pathway
ADH
epinephrine
45
Which hormones exclusively use the tyrosine kinase pathway
insulin
46
Provide a detailed description of the tyrosine kinase receptor signalling pathway using insulin receptor as an example
1. insulin binds to specific transmembrane protein
2. upon binding, receptor undergoes conformational change that allows 2 insulin receptor molecules to come together to form an active complex
3. activated receptor adds phosphate group to specific tyrosine residues on itself
4. phosphotyrosine residues on activated receptor act as docking site for other proteins
5. Docked proteins activate intracellular signalling pathways
- PI3K = activates glucose uptake & glycogen synthesis
- MAPK = stimulates cell growth, differentiation and proliferation
47
Give examples of lipid soluble hormones
oestrogen
progesterone
testosterone
cortisol
aldosterone
thyroid hormones
48
lipid soluble hormones pass through cell membrane & interact directly with hormone receptors. Describe how cortisol affects the cell upon arrival
1. cortisol easily dissolves through cell membrane
2. Inside the cell, cortisol binds to specific intracellular receptor (glucocorticoid receptor) which becomes activated upon binding
3. GR undergoes conformational change allowing it to act as a transcription factor
4. this exposes nuclear localisation signal enabling receptor-hormone complex to enter cell's nucleus
5. in nucleus it interacts with specific regulatory regions of DNA (GREs)
6. This interaction can stimulate/inhibit expressions of genes (through transcription)
biological effects:
- regulation of blood glucose levels
suppression of immune response
- suppression of inflammatory response
- modulation of metabolism
49
Are water-soluble or lipid soluble hormones faster at exerting their actions on target cells? why?
Water soluble
Act on cell surface receptor (instead of intracellular)
mediated by cAMP which rapidly propagates signals inside cells
Cause rapid, short lived effects
50
Label the kidney
51
label the nephron
52
Where in nephron are:
Bowmans capsule
Glomerulus
Loop of Henle
PCT
DCT
collecting ducts
Cortex:
- PCT
- Bowmans capsule
- Glomerulus
- DCT
Medulla:
- Loop of Henle
- Collecting ducts
53
Describe filtration in kidney
Ultrafiltration occurs between capillaries of glomerulus & Bowman’s capsule
Is filtration under pressure, pressure increase caused by having narrower efferent arteriole
Filtration depends on molecule size & charge. E.g., glucose, electrolytes, waste products allowed through large proteins are not
How much plasma gets filtered is Glomerular Filtration Rate (GFR) which depends on renal blood flow/pressure & no. of available nephrons.
54
Where does most reabsorption occur in kidney
proximal convoluted tubule
55
What gets reabsorbed in the proximal convoluted tubules
Glucose
Sodium
Water
Amino acids
Salt
Urea
56
Fill in the glomerular ultrafiltrate table
57
What hormones influence water resorption
ADH pituitary (vasopressin)- water channels & urea (for medullary concentration gradient) – helps reabsorb water
Aldosterone (RAAS) – preserves water by absorbing Na+ in exchange for K+ and H+
58
What do you lose in the ascending and descending loop of henle
Lose water in descending loop & solutes in ascending loop
59
What is normal blood glucose concentration
“Normal”: 3.5 to 5.5 mmol/L (dog)
>14mmol/L – usually diabetes mellitus
Glycosuria usually starts to occur at ~approx. double normal blood glucose concentration (10-12mmol/L)
60
What is transport maximum in kidneys
Transport maximum is point at which all glucose transporters in proximal convoluted tubule are saturated & thus all remainder glucose stays in tubule/urine…
Lowers concentration gradient so more water is lost – reason why patients w diabetes pee loads
61
What is osmotic diuresis
increased urination due to presence of certain substances in kidney ultrafiltrate
62
What can cause osmotic diuresis
Glucose in tubule acts as an osmolyte
- Draws water into tubule by osmosis
- Greater urine production
Can be due to salts rather than glucose
Therapeutic osmotic diuresis (Mannitol) – increase osmolarity to attract water
63
What is azotaemia
64
What is Urine specific gravity
65
What is diabetes insipidus
66
Describe how the adenohypophysis/anterior pituitary is controlled by the hypothalamus
releasing factors from hypothalamus circulate via hypothalamo-hypophyseal portal system to adenohypophysis and act on specific target cells (BBB absent in this area)
Specific target cells release stimulating hormones which circulate to target organs
67
Describe how the posterior pituitary/neurohypophysis is controlled by the hypothalamus
Axons from supraoptic and paraventricular nuclei in hypothalamus form supraopticohypophyseal & paraventriculohypophyseal tracts
These tracts descend into the neural lobe via the infundibulum
68
What is the function of the pineal gland
controls circadian rhythms
controls breeding seasons
mediates courtship/breeding behaviours
linked with seasonal hair/feather colour changes
69
what is the function of melatonin from the pineal gland?
modulates sleep patterns
inhibits or stimulates repro cycles in seasonal breeders
- affects release of LH & FSH
70
What cells are found in the thyroid gland
Follicular cells:
- secrete thyroid hormones T3 and T4 by proteolysis
- metabolic effects
Parafollicular/C-cells:
- secrete calcitonin
- lowers blood calcium
71
How is thyroid hormones stored in thyroid gland
stored extracellularly bound to thyroglobulin
Follicular cells surround and contain the thyroglobulin
72
What are the cells found in the parathyroids and what do they secrete
Chief/principal cells
Produce parathyroid hormone (PTH) => raises blood calcium
73
Label the layers and secretions of adrenal gland
74
Describe the effects of the corticoids produced from the adrenal cortex
mineralocortioids - targets kidney to control Na and water reabsorption - alter blood pressure
glucocorticoids - effect metabolism
androgens (oestrogen, testosterone etc.) - effects metabolism
75
Describe the blood supply to the hypophysis/pituitary gland
Sits in Circle of Willis - arterial supply to whole brain
76
Describe the blood supply to the thyroid gland
Arteries:
- cranial and caudal thyroid arteries
Veins:
- thyroid veins
77
Describe blood supply to the adrenal glands
Branches from aorta, renal, lumbar and cranial mesenteric arteries
blood draining the cortex enters medullary sinusoids, mixes with blood in medullary cells, central medullary veins collect blood, drained into caudal vena cava
78
How do lipid soluble hormones affect cell at level of nucleus
hormone diffuses into cell across plasma membrane
binds to receptor
Complex diffuses into nucleus and alters DNA => protein synthesis => biological response
79
80
why might an animal that has dramatic polyuria end up with low blood urea concentration
81
Why do these conditions cause polyuria
82
83
How does hypoadrenocorticism result in a dangerously high blood potassium level
84
What is digestion
Process in alimentary canal by which food is broken up
Physically by teeth
Chemically by action of enzymes
Converted into substance suitable for absorption & assimilation into body
Co-ordinated process that extracts nutrients out of food & makes them available for absorption inside gut into blood stream & lymphatic circulation
85
describe carbohydrates
Chains made of single units called monosaccharaides
Monosaccharaides are joined together to form carbohydrates or polysaccharides (via condensation reaction)
Products of carbohydrate digestion are; glucose, fructose & galactose
These are small enough to pass into the capillaries - and pass via the hepatic portal vein to the liver.
86
What is the fate of glucose, fructose and galactose
Glucose is readily available & usable by cells throughout body as substrate for energy production
In liver, fructose & galactose are converted into glucose
87
What happens to excess glucose
In liver, excess glucose is converted (anabolised) into glycogen
Liver glycogen acts as storage which can be used to ‘top up’ circulating glucose levels when needed
The liver has a limited capacity to store glycogen
Glucose can also be stored as glycogen in muscle or combined with amino acids to make fats in body
88
What are proteins
Large molecules which can’t be absorbed without being broken down
Made from monomers called amino acids
Amino acids are joined in long chains by peptide bonds to make proteins
Different proteins are created by no. & combination of amino acids in chain
Around ten are essential
- they cannot be manufactured by the body.
89
Why do animals need protein in diet
Protein essential in diet for growth & maintenance of body tissues
can also be used for energy, although less efficient than fat or carbohydrate metabolism
90
What is the fate of amino acids (protein digestion)
Amino acids are absorbed into intestinal capillaries & transported to liver via hepatic portal vein
In liver they may be modified to keto acids & plasma proteins (e.g. albumin/globulin)
Most amino acids enter systemic circulation via caudal vena cava unaltered
In cells, amino acids are synthesised into different proteins for intracellular function (eg intracellular membranes) or for export from cell (eg enzymes)
91
What are lipids
Fats which made up from small units called triglycerides
Each triglyceride/ triacylglycerol (TAG) is made from molecule of glycerol & 3 fatty acid chains
The fatty acid chains give the fat its properties
- saturated or unsaturated
Saturated fatty acids have less uses in body as they have less double bonds in structure which makes them less reactive.
92
Describe the fate of triglycerides
Triglycerides too large to be absorbed, broken down by digestion into monoglycerides & then into glycerol & free fatty acids
First, bile salts emulsify lipid to then be hydrolysed by enzymes into monoglycerides which are dissolved into micelles
Micelles freely enter intestinal cells where triglycerides are re-synthesised from glycerol & 3 fatty acids, together with cholesterol & packaged into lipoprotein particles (chylomicrons)
93
What controls the glucose supply
Liver is responsible for regulating blood glucose supply
2 hormones, insulin & glucagon, jointly regulate storage & recycling of blood sugar
They are produced by Islets of Langerhans in pancreas:
- ß cells secrete insulin
- α cells secrete glucagon
- δ cells secrete somatostatin
Insulin & glucagon have opposing effects so work together to maintain balance
94
fill in the glucose regulation diagram
95
describe the fate of protein
Excess amino acids are disposed of via deamination
Deamination releases ammonia which is highly toxic, immediately converted into urea by liver
As glycogen levels deplete, skeletal muscle protein is broken down as substrate for gluconeogenesis
Amino acids are deaminated to yield ammonium (NH4+) & carbon skeleton.
After deamination, amino acids enter energy production pathway as pyruvate, acetyl CoA, or components of TCA cycle
96
Describe the fate of lipids
Chylomicrons carried by lacteals into lymphatic system & bloodstream, to be stored in adipose tissue, without first going to liver
Some chylomicrons circulate back to liver where they are stored, converted to other molecules or used as an energy substrate
- Fats only stored in liver when there is overwhelming influx
- Negative welfare state
Fatty acids are stored primarily in adipocytes as triacylglycerol
- Adipocytes found mostly in abdominal cavity & subcutaneous tissue
If animal's energy intake exceeds body's requirements, fat is stored in fatty deposits around body
97
describe lipids as an energy source
In absence of glucose, fat is broken down into TAG which circulates to liver to be used as source of energy
As by-product of fat metabolism ketone bodies are produced by liver
Ketones are also source of energy but may accumulate in blood & pass into urine
If very high concentrations of ketones are formed, clinical condition (ketosis) occurs
Ketosis common in dairy animals as they need large energy intake but bad at tolerating ketones
Ketone bodies are acidic and high levels can be fatal.
98
What are the 2 metabolic lipase enzymes
Hormone sensitive lipase (HSL)
- Hydrolyses; either fatty acid from triacylglycerol molecule, freeing fatty acid & diglyceride
- or fatty acid from diacylglycerol molecule, freeing fatty acid & monoglyceride
- Mechanism of release of lipid from storage
Lipoprotein lipase (LPL)
- Degrades circulating triglycerides in bloodstream to be taken up by tissues
- Facilitates storage of lipid into tissues
99
What is metabolic rate
Rate at which living organisms expend energy or convert energy into food
100
What regulates metabolic rate and how does it do it
Thyroid, under hypothalamus (& pituitary) influence, regulates basal metabolic rate
It achieves this through:
- Speeding up metabolism and development
- Increasing metabolic use of energy
- Increasing digestion rate in the intestine (esp. glucose)
- Down-regulating insulin receptors
- Increasing glycogenolysis and gluconeogenesis
- Increasing lipogenesis in adipocytes.
101
define metabolism
102
What are ras-oncogenes?
group of cells whose normal function is to regulate cell growth and differentiation
Can cause cancer when overactivated
103
Why do animals need to keep their blood sugar levels at a minimum level, even between meals?
energy source
metabolic function
regulation of hormones
stable cellular function
preventing hypoglycaemia
muscle function
104
What is glycolysis
105
What influence does insulin have in absorptive phase on macronutrients in liver
glycogen synthesis (glycogenesis) - stimulates liver to take up glucose from blood & convert it into glycogen
inhibition of gluconeogenesis
- prevents liver from releasing glucose into liver
106
What influence does insulin have in absorptive phase on macronutrients in fat
lipogenesis
- promotes synthesis of triglycerides from glucose
inhibition of lipolysis
- inhibits breakdown of stored fat into fatty acids which prevents their release into blood stream & favors fat storage
107
What influence does insulin have in absorptive phase on macronutrients in muscle
glucose uptake
- allows them to use it for energy
amino acid uptake
- allows it to be used for protein synthesis and muscle repair
108
What influence does insulin have in inter-prandial (post-absorptive) phase on macronutrients in muscle
glucose uptake
- allows glucose to be conserved for tissues with higher energy demands
109
What influence does insulin have in inter-prandial (post-absorptive) phase on macronutrients in liver
glycogenolysis
- liver converts glycogen into glucose to release into bloodstream
gluconeogenesis inhibition
- prevents liver from producing excessive glucose
110
What influence does insulin have in inter-prandial (post-absorptive) phase on macronutrients in fat
lipolysis
111
What is the difference between glycogenolysis and gluconeogenesis as methods of creating glucose from stored resources
112
What are the hypothalamic inputs
Direct sensing by receptors
Indirect humoral sensing (via blood)
- Receptors for circulating hormones
Indirect neural sensing (via nerves)
- Visceral & somatic sensory nerves - detect pressure
- Limbic system (emotions) – motion system
- Reticular activating system – retina
113
describe thermoreceptors as a direct hypothalamic input
Neurons in anterior hypothalamus
- Respond to heat...thermoregulation cooling center
- Respond with peripheral vasodilation & sweating
Neurons in posterior hypothalamus
- Respond to cold...thermoregulation heating center
- Respond with peripheral vasoconstriction, piloerection & shivering
114
describe osmoreceptors as a direct hypothalamic input
Respond to increase in blood osmolarity (haemoconcentration; dehydration)
Response:
- ADH release from supraoptic nucleus
- Secreted via posterior pituitary
- Kidneys concentrate urine (retain water)
- Stimulate neurons within thirst centre in lateral hypothalamus
115
What are the satiety centre and appetite centre
Satiety centre
- Responds to high glucose levels
- Inhibits eating by releasing leptin
Appetite centre
- Responds to low glucose levels
- Stimulates eating by releasing Ghrelin
116
What is the biological clock
Causes you to go to sleep or wake up
Light sensed by retina
Transmitted via nerve pathways
Arrive at hypothalamus
Specifically suprachiasmatic nucleus (SCN) (biological clock)
Stimulates pineal gland (to make melatonin) & other pathways
117
Describe the secretory neurons of the hypothalamus
screte ADH and oxytocin
Cell bodies in the nuclei of hypothalamus
- Supraoptic nucleus (SON)
- Paraventricular nucleus (PVN)
Axons descend into the posterior pituitary
Nerves terminate on blood vessels & release hormone directly into circulation
Posterior pituitary is storage site, collection of nerves & not true endocrine gland
118
Name some hypothalamus releasing hormones
CRH
TRH
GHRH
GnRH
PRL-RH
cause pituitary gland to release hormones which then cause target organ to release hormones into bloodstream
119
Name some hypothalamus inhibitory hormones
GHIH
GnIH
dopamine
120
What are the anterior pituitary hormones
Thyroid-stimulating hormone (TSH/thyrotropin)
Adrenocorticotropin hormone (ACTH / corticotropin)
Growth hormone (GH / somatotropin)
Prolactin (PRL)
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
121
What are the 5 anterior pituitary cell types and the hormone they produce
122
What hormones regulate GH (somatotropin) secretion
GH-releasing hormone (GHRH)
Somatostatin (also called GHIH)
Ghrelin (hormone from the stomach)
123
What are the functions of growth hormone
Stimulates IGF-1 secretion from liver
Growth
Stimulates protein synthesis
Stimulates lipolysis
Inhibits glucose utilization
124
What regulates gonadotropes
GnRH from the hypothalamus
Negative feedback loop
125
What are closed vs open feedback loops
Closed loop
- Target cells secrete hormones that affect their own secretion
- Feedback regulation (usually negative)
Open loop
- No direct feedback
- Stopped by removal of stimulus or depletion of biochemicals
- Example: Stimulation of milk let down
126
What are positive feedback loops
Positive feedback loops are rare
When secretion of hormone increases in response to feedback from organ
- An amplification process
Example:
- Oxytocin causes uterine contraction
- Uterus stretched during delivery
- Nervous impulses to the hypothalamus
127
What are negative feedback loops
The most common type of feedback
Short feedback loop
- Hormone from pituitary gland(ACTH)
- Feedback to hypothalamus
- Less CRH from hypothalamus
Long feedback loop
- Hormone from gland (cortisol)
- Feedback to hypothalamus
- Can also feedback on pituitary gland
128
What is the trigger for shedding (moulting) if winter hair coat in horses
increase in photoperiod triggers release of melatonin and prolactin which play role in hair growth cycles
129
Fill in the hypothalamic-pituitary-adrenal (HPA) axis
130
Fill in the hypothalamic-pituitary-gonadal (HPG) axis for females
131
Fill in the hypothalamic-pituitary-gonadal (HPG) axis for males
132
Fill in the hypothalamic-pituitary-thyroid axis
133
What hormones does the posterior pituitary gland produce
anti-diuretic hormone
oxytocin
134
Describe the actions of ADH
Acts on distal tubule & collecting duct
Increases permeability to water
More water moves out of tubule, resorbed
Urine volume decreases
Urine concentration increases
135
What are aquaporins and where are they
Water channels in proximal tubule, present on all membranes
In the distal tubule and collecting ducts:
- Always present in baso-lateral membranes
- Only present in apical membranes when ADH present
136
How does ADH affect aquaporin density on tubule surfaces
Increases aquaporin density
Aquaporin-2 (AQP-2) is under ADH control
1. ADH binds to receptors
2. Activation of adenyl cyclase
3. Production of cAMP
4. Vesicles containing aquaporins move to cell surface
Inserted via exocytosis
Proportional to plasma ADH concentration
Removed via endocytosis
137
What detects dehydration in the body
Osmoreceptors
- Within the hypothalamus
- Respond to increase in osmolarity of extracellular fluid (ECF)
- More ADH released
- More water conserved
Stretch (or volume) receptors
- Respond to large changes (10% decrease in blood)
- Decrease in distension detected (caused by smaller blood volume)
- Nervous impulses to the hypothalamus
- More ADH released
- Water conserved
138
What is osmolarity
Osmolarity = no. of dissolved particles per unit volume
More concentrated = higher osmolarity
139
Describe the overall hydration regulatory system
Osmoreceptors are the most sensitive
Thirst stimulation is major method of correcting dehydration
Release of ADH helps to conserve water
Volume receptors in veins & atria only triggered by large decrease in volume
However, large amounts of ADH released when triggered (emergency response!)
140
What causes diabetes insipidus
ADH dysregulation
141
What are the 2 types of diabetes insipidus
Neurogenic diabetes insipidus
- Inadequate ADH release from pituitary
Nephrogenic diabetes insipidus
- Inadequate response within the kidney
142
How is diabetes insipidus diagnosed
Injection of exogenous ADH
- Concentrated urine: neurogenic
* ie compensates for failure to produce ADH
- Dilute urine: nephrogenic
* ie kidney fails to respond to extra ADH
143
What is the role of oxytocin with respect to lactation
Oxytocin stimulates milk let down
Acts on smooth muscle cells
- Uterine muscle during parturition
- induces contraction of alveoli of mammary glands
Release regulated by neuronal reflexes
144
Describe the neuronal transmission of lactation
High density of sensory nerve fibers in teats detect suckling or preparation for milking
Impulses transmitted via superficial sensory pathways & inguinal nerve
Afferent sensory neurons enter lumbar segments of spinal cord
Ascend the spinal cord sensory tracts
To thalamus, influence cell bodies of neuroendocrine cells
Secretion of oxytocin from nerve endings in posterior pituitary gland into circulation
Sensory input: smell, sounds, sight of calf
145
What are the effects of oxytocin on the mammary gland
Increases pressure within alveoli
Reduces resistance in excretory ducts
Reduces resistance in teat canal
Result: Increased milk outflow
146
Describe the role of oxytocin during pregnancy
Preparation for delivery
Stimulate milk let down
147
What is the neuroendocrine reflex during parturition
Stimulate sensory nerve endings in cervix
Afferent nerve impulses to hypothalamus
Neuroendocrine cells of paraventricular & supraoptic nuclei depolarize
Secrete oxytocin from pars nervosa (posterior pituitary gland)
Enters blood circulation
Act on oxytocin receptors of myometrium
Strong uterine contractions
148
What is the clinical relevance of oxytocin in parturition
Oxytocin can be administered to induce parturition in horses
Oxytocin will induce contractions & help expel retained placenta
Used to clear fluid from the uterus (metritis)
149
What volume of fluid must dogs & cats consume to be considered polydipsic
150
What volume of urine must cats and dogs produce to be considered polyuric
50ml/kg/day
151
Name 2 stimuli that may cause ADH release
increased plasma osmolarity
low blood volume
152
Name causes of central diabetes insipidus
trauma
idiopathic
brain tumour
153
Name 2 endocrinopathies that cause secondary neprhogenic diabetes insipidus
hypercalcaemia
hypoadrenocorticism
154
Name non-endocrine diseases that cause secondary neprhogenic diabetes insipidus
infections with bacteria that produce toxins that interfere with ADH action
e.g. pyelonephritis, pyometra
155
What would you expect to happen to urine specific gravity of a dog given synthetic ADH if it had central diabetes insipidus
increase - kidneys absorb more water so urine becomes less diluted
156
What would you expect to happen to urine specific gravity of a dog given synthetic ADH if it had primary nephrogenic diabetes insipidus
remain low - kidneys are unable to respond to ADH regardless of amount of hormone
157
What are the components of the diencephalon?
epithalmus
thalmus
hypothalamus
158
What are the nuclei of the hypothalamus and what are their functions?
Paraventricular (PVN) - oxytocin, ADH, TRH, CRH
Supraoptic (SON) - oxytocin, ADH
Suprachiasmatic (SCN) - circadian rhythm
Lateral (LN) - arousal, hunger
Arcuate (AN) - energy, GnRH
Mammillary - wakefulness
159
how does the hypothalamus act as a biological clock?
light sensed by retina, nerve signal arrives at hypothalamus (suprachiasmatic nucleus)
Stimulates pineal gland (melatonin)
160
What connects the hypothalamus and the anterior pituitary?
hypophyseal portal veins
161
What is tonic and episodic secretion?
tonic = constant secretion with increases and decreases
Episodic = pulses/surges
162
what is the function of growth hormone?
Stimulates IGF-1 secretion from liver
Growth
Stimulates protein synthesis
Stimulates lipolysis
Inhibits glucose utilisation (inhibits insulin)
163
What causes gigantism/giantism?
pituitary hyperactivity or neoplasia before adolescence
164
What causes acromegaly?
pituitary disorders after adolescence
Leah ENI
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