Endocrine System 1

Question 1

What is Homeostasis

Answer 1

It is the process of maintaining a constant internal environment despite changing conditions.

“homeostasis”, regulation of the internal environment

Question 2

Is Homeostasis an Equilibrium?

Answer 2

NO!
It is the process of maintaining a constant internal environment despite changing conditions.

“homeostasis”, regulation of the internal environment

Question 3

Set Point

Answer 3

Oscillation around a setpoint mean that a set point, known as our target point, can have a range

Ex. With the fish tank example, if the setpoint was 30, anything between 29 to 31 degrees is within the normal functioning range

Once we deviate from the normal range, that is when a response turns on, until the range is reestablished at which point the response is turned off

Question 4

Stabilizing response

Answer 4

Some sort of initial stimulus takes you away from the set point

The body (or water tank) will elicit a response that will decrease the effect of that initial stimulus

Once everything is stabilized a signal is sent back to stop this whole loop from forming again

Question 5

Negative Feedback Loop

Answer 5

Negative feedback is able to get the body or the system back to homeostasis

One thing cancels another essentially

Question 6

Positive Feedback

Answer 6

This is when a stimulus starts a response, but for some reason, at that point, you stimulate the response further and further to reinforce the effect of that stimulus

It can be turned off by outside factors

It is a reinforcing loop that is the opposite of reaching homeostasis; it is used for change (Ex. giving birth)

Question 7

Regulation of Cortisol Negative Feedback Loop Example

Answer 7

Cortisol is going to be somehow stimulated to be released via the set of steps seen below;

1. The hypothalamus is going to release a stimulating hormone
2. Hormone will stimulate the anterior pituitary which will in turn stimulate the ACTH hormone
3. ACTH will travel to the adrenal cortex and release cortisol

The negative feedback loop comes in to play;

When there is enough cortisol in the body, you want the process to stop, so you stay within the range of the setpoint

Once the body sense that there is enough, it starts to suppress the upstream release

Cortisol suppresses the release of ACTH and the release of in the hypothalamus of CRH to stop producing cortisol

Question 8

Positive Feedback Example

Answer 8

When it time for the baby to come out, the baby drops lower in the uterus and pushes on the cervix initiating labor

The stretching of the cervix is the initiating stimulus

It stimulates the release of a hormone oxytocin, which causes the uterus to contract

The more the cervix contracts, the more the baby pushes against the cervix, stimulating more oxytocin release, and on and on.

It only stops when the baby is finally delivered

Question 9

Maintaining homeostasis and other body functions requires…

Answer 9

intercellular communication

Question 10

Local Control

Answer 10

Communication that happens in one location
- Gap Junctions
- Contact-Dependent Signals
- Autocrine

Question 11

Gap Junctions

Answer 11

Holes that connect the cells to the each other so that there is free passage of molecules and ion

Often seen in cardiac muscles

Question 12

Contact-Dependent Signals

Answer 12

Cells next to each other recognize changes in each other

Important in the immune system

Question 13

Autocrine

Answer 13

Idea is that one molecule can be secreted from one cell but then act on the same cell or the neighboring ones

Cytokines and histamines

Question 14

Long Distance Communication

Answer 14

The nervous system is one way that the body can communicate in long distances
- You have neurotransmitters that are secreted by neurons that diffuse across a small gap to the target cell to elicit a response and often a series of these is going to help us reach the distant target

The endocrine system is the second major system in the body for long-distance communication

An endocrine cell is able to release a hormone that then travels through the bloodstream all the way down to the target cell

This hormone doesn’t have an effect on every single cell that it encounters because the hormone needs to find the right receptor

Question 15

Neurohormones

Answer 15

Are another class known as neuroendocrine

These are secreted by neurons often in the hypothalamus, that then release hormones into the bloodstream to eventually find their target cells

Question 16

Reflexes

Answer 16

This idea that we’re going to have long distance communication in the body

A number of different factors play a role in this
- Simple reflexes are mediated either by the nervous or the endocrine system
- Complex reflexes are mediated by both systems and go through several integrating systems

Question 17

What is the difference between afferent and efferent neurons?

Answer 17

Afferent neurons carry signals to the CNS (sensory input).

Efferent neurons carry signals away from the CNS to effectors (muscles/glands).

Question 18

What do sensory neurons do?

Answer 18

Detect and transmit information about stimuli (e.g., touch, temperature) to the CNS.

Question 19

What is the difference between local control and reflex control?

Answer 19

Local control acts within a tissue (e.g., local vasodilation). Homeostatic control restricted to a tissue or cell, using paracrine or autocrine signals; response is limited to the area of change.

Reflex control is coordinated by the CNS or endocrine system for body-wide responses.

Question 20

What is a simple endocrine reflex?

Answer 20

A hormone release triggered by a stimulus and regulated by negative feedback — e.g., insulin secretion in response to high blood glucose.

Question 21

What are the two basic patterns of control mechanisms?

Answer 21

Local control and long-distance (reflex) control.

Question 22

What are the three components of a control system?

Answer 22

Input signal, integrating center, output signal.

Question 23

Give an example of local control

Answer 23

Low O₂ in tissues → cells lining small blood vessels detect change → release chemicals → relax vessel muscles → increase blood flow & oxygen.

Question 24

Define reflex control

Answer 24

Long-distance homeostatic control using the nervous system, endocrine system, or both.

Question 25

What are the two main parts of a physiological reflex?

Answer 25

Response loop (stimulus → response) and feedback loop.

Question 26

What is feedforward control?

Answer 26

Anticipatory response that starts a control loop before a change occurs (e.g., salivation reflex before eating).

Question 27

What are biological rhythms?

Answer 27

Predictable, repeating patterns in regulated variables (e.g., circadian rhythm).

Question 28

Difference between acclimatization vs. acclimation?

Answer 28

Acclimatization = natural adaptation to environmental conditions. Acclimation = laboratory-induced physiological adjustment.

Question 29

What are the two types of physiological signals?

Answer 29

Electrical (changes in membrane potential) and chemical (ligands secreted into ECF).

Question 30

What are target cells?

Answer 30

Cells that respond to electrical or chemical signals.

Question 31

What are CAMs?

Answer 31

Cell adhesion molecules; membrane proteins for contact-dependent signaling (juxtacrine).

Question 32

Paracrine vs. Autocrine signals?

Answer 32

Paracrine = acts on nearby cells. Autocrine = acts on the same cell that secreted it.

Question 33

How does long-distance communication occur?

Answer 33

Nervous system (electrical + neurocrine chemicals) and endocrine system (hormones in blood).

Question 34

What are the three types of neurocrine molecules?

Answer 34

Neurotransmitters (fast, local), neuromodulators (slower, paracrine/autocrine), neurohormones (secreted into blood).

Question 35

What are cytokines?

Answer 35

Chemical signals involved in immune responses; can act locally (auto/paracrine) or systemically like hormones.

Question 36

What are Cannon’s four postulates?

Answer 36

Nervous system preserves internal fitness. Some systems under tonic control. Some systems under antagonistic control. One chemical signal can have different effects in different tissues.

Question 37

What is tonic control?

Answer 37

Ongoing (continuous) neural activity allowing modulation up or down.

Question 38

What is antagonistic control?

Answer 38

Opposing influences regulate processes (e.g., sympathetic vs parasympathetic, insulin vs glucagon).

Question 39

Sympathetic vs Parasympathetic roles?

Answer 39

Sympathetic = fight/flight (↑HR, dilate pupils, inhibit digestion). Parasympathetic = rest/digest (↓HR, constrict pupils, stimulate digestion)

Question 40

What are the three components of a reflex pathway?

Answer 40

Input → Integrating center → Output

Question 41

What is the role of sensors in reflex pathways?

Answer 41

Detect stimulus once threshold is reached, send input signals.

Question 42

Example of endocrine reflex for blood glucose?

Answer 42

High glucose → pancreatic beta cells detect & release insulin → cells uptake glucose → blood glucose decreases → negative feedback reduces insulin secretion.

Question 43

What are hormones?

Answer 43

Chemical signals secreted by endocrine glands or cells into the blood, distributed to distant targets, and effective at very low concentrations.

Question 44

What distinguishes hormones from other chemical signals?

Answer 44

They travel in the blood and act on distant targets, unlike local signals.

Question 45

What are neurohormones?

Answer 45

Hormones secreted by neurons into the blood for systemic distribution.

Question 46

What are hydrophilic hormones?

Answer 46

Water-soluble, lipophobic hormones that cannot cross plasma membranes. Examples: peptide/protein hormones, catecholamines.

Question 47

What are hydrophobic hormones?

Answer 47

Lipid-soluble, lipophilic hormones that cross membranes easily but require carrier proteins in blood. Examples: steroid and thyroid hormones.

Question 48

How are hydrophilic hormones synthesized and released?

Answer 48

Made in advance, stored in vesicles, released by exocytosis, transported dissolved in plasma.

Question 49

How are hydrophobic hormones synthesized and released?

Answer 49

Made on demand, not stored, released by diffusion, transported bound to carrier proteins (>99%).

Question 50

What are the three main types of hormones?

Answer 50

Peptide/protein (3+ amino acids), steroid (cholesterol-derived), and amine (single amino acid-derived).

Question 51

Properties of peptide/protein hormones?

Answer 51

Water soluble, short half-life, stored in vesicles, released by exocytosis, bind to membrane receptors.

Question 52

Examples of peptide hormones?

Answer 52

Insulin, glucagon, oxytocin, ADH.

Question 53

What are the stages of peptide hormone synthesis?

Answer 53

Gene transcription (mRNA) → translation (preprohormone) → cleavage in ER (prohormone) → processing in Golgi → stored in vesicles → cleaved to active hormone + co-peptide → released by exocytosis.

Question 54

What is a preprohormone?

Answer 54

An inactive precursor with a signal peptide and one or more hormone segments. Proteolytic enzymes (like prohormone convertases) process these precursors into active hormones.

Question 55

Insulin is degraded in the body extremely quickly and is difficult to measure because of this. How else could we indirectly measure insulin release?

Answer 55

A) Measure preproinsulin protein B) Measure C-peptide levels Because C-peptide is cleaved off, so the amount of C-peptide is related to the actual amount of insulin C) Measure fatty acid levels D) Measure beta cell mass

Question 56

Properties of Steroid Hormones

Answer 56

Derived from cholesterol, synthesized on demand, diffuse across membranes, lipid-soluble, bound to carriers in blood, long half-life, bind to intracellular receptors.

Question 57

Examples of steroid hormones?

Answer 57

Estrogen, cortisol, aldosterone. In the ovaries have different enzymes to add or take out different portions of this enzyme to create an estrogen. In a different organ (ex. The adrenal cortex) enzymes will create aldosterone or cortisol

Question 58

Why can’t steroid hormones be stored in vesicles?

Answer 58

They are lipophilic and diffuse freely through membranes.

Question 59

What are amine hormones derived from?

Answer 59

Amino acids tryptophan or tyrosine.

Question 60

Tryptophan derivative hormone?

Answer 60

Melatonin (pineal gland, regulates circadian rhythms, immune modulation, antioxidant).

Question 61

Tyrosine derivative hormones?

Answer 61

Catecholamines (epinephrine, norepinephrine, dopamine → act like peptides) and thyroid hormones (T3, T4 → act like steroids).

Question 62

Properties of catecholamines?

Answer 62

Synthesized in adrenal medulla, stored in vesicles, released by exocytosis, lipophobic, bind to membrane receptors.

Question 63

How do endocrine cells release hormones?

Answer 63

By directly sensing stimuli (e.g., ions, nutrients, neural signals).

Question 64

Mechanisms that trigger hormone release?

Answer 64

Act through intracellular pathways to: change the membrane potential of the cell through ions passing in an out increase in free cytosolic Ca2+ depending on the cell type change enzymatic activity increase the transport of hormone substrates into the cell – so by increasing the transport inside the cell, that can be a signal that the hormone needs to be activated alter transcription of genes coding for hormones or for enzymes needed for hormone synthesis promote survival and in some cases growth of the endocrine cell

Question 65

Example of glucose-stimulated insulin release?

Answer 65

The beta cell stores insulin, a peptide hormone, in secretory vesicles. When blood glucose rises, glucose enters the beta cell via GLUT2 receptors. Inside the beta cell, glucose metabolism (glycolysis and respiration) increases → raises ATP levels. The increased ATP/ADP ratio in the beta cell causes ATP-sensitive potassium (K⁺) channels to close. Closing these channels reduces K⁺ efflux, leading the beta cell membrane to depolarize. Depolarization opens voltage-gated calcium (Ca²⁺) channels in the beta cell. Calcium influx acts as a signal for vesicles in the beta cell to exocytose insulin. Insulin is released into the bloodstream to help lower blood glucose levels.

Question 66

Sulfonylurea blocks KATP channels, what effect would this have?

Answer 66

Enhances insulin secretion by keeping Ca²⁺ channels open

Question 67

How does the hypothalamic-pituitary axis regulate hormones?

Answer 67

Hypothalamus releases hormones → anterior pituitary secretes its hormones → stimulates peripheral endocrine glands → glands secrete final hormones → negative feedback to hypothalamus & pituitary.

Question 68

Which pituitary lobe produces hormones?

Answer 68

Anterior pituitary (endocrine tissue).

Question 69

Does the posterior pituitary synthesize hormones?

Answer 69

No, it only releases hypothalamic hormones (e.g., oxytocin, ADH).

Question 70

What is synergism in hormone action?

Answer 70

Two or more hormones act together for an amplified effect (e.g., FSH + testosterone in sperm production).

Question 71

What is permissiveness in hormone action?

Answer 71

One hormone enhances the effect of another (e.g., estrogen prepares uterus for progesterone)

Question 72

What is antagonism in hormone action?

Answer 72

One hormone opposes the action of another (e.g., insulin ↓ blood glucose, glucagon ↑ blood glucose).

Question 73

How do glucagon, epinephrine, and cortisol interact in blood glucose regulation?

Answer 73

Together they show synergistic and permissive effects → greater and longer-lasting increase in glucose than alone

Question 74

How do hormones signal inside cells?

Answer 74

Hormone binds to receptor → receptor changes conformation/activity → alters intracellular signaling pathways → leads to changes in protein synthesis (slow) or protein modification (fast).

Question 75

What type of hormones bind intracellular receptors?

Answer 75

Hydrophobic (lipid-soluble) hormones that diffuse through membranes (e.g., steroids, thyroid hormones).

Question 76

What type of hormones bind membrane receptors?

Answer 76

Hydrophilic (water-soluble) hormones that cannot cross membranes (e.g., peptides, catecholamines).

Question 77

What characteristics do all receptors share?

Answer 77

Large proteins, grouped in families, variable abundance (500–100,000 per cell), can be activated/inhibited, specific, saturable, high-affinity, reversible binding, located in membrane/cytoplasm/nucleus.

Question 78

What happens when receptors become saturated?

Answer 78

Increasing hormone concentration no longer increases the response (plateau effect).

Question 79

Hormone A binds to receptor B which causes response C. The concentration of hormone A doubles in the body causing a doubling in response C. The concentration of hormone A doubles again, but this time no change in response C. What could be happening?

Answer 79

A) Receptor B is saturated B) This is an example of positive feedback C) This is an example of neutral feedback D) Hormone A is no longer specific to receptor B Answer = A

Question 80

What are the two main types of receptors?

Answer 80

Intracellular receptors – bind lipid-soluble hormones (cytosolic or nuclear). Directly alter gene transcription → genomic effects. Plasma membrane receptors – bind water-soluble hormones. Includes GPCRs, receptor-enzymes, receptor-channels, integrins.

Question 81

How do peptide hormones act?

Answer 81

Bind surface receptors → activate intracellular signaling via second messengers (fast).

Question 82

How do steroid hormones act?

Answer 82

Enter cell → bind internal receptors (cytoplasm/nucleus) → alter gene transcription → effects take hours to days.

Question 83

What are hormone response elements (HREs)?

Answer 83

Specific DNA sequences where hormone-receptor complexes bind to regulate gene transcription (activation or repression).

Question 84

Structure of GPCRs?

Answer 84

Large membrane-spanning proteins with cytoplasmic tail linked to a G protein (α, β, γ subunits). alpha has 3 subtypes, SIQ

Question 85

Main second messengers used by GPCRs?

Answer 85

cAMP, DAG, IP3, Ca²⁺ G protein-coupled adenylyl cyclase-cAMP system is the signal transduction system for many protein hormones G protein-coupled receptors use some lipid second messengers: e.g., diacylglycerol (DAG) and inositol trisphosphate (IP3)

Question 86

When G proteins are activated, they

Answer 86

Open ion channels in the membrane Alter enzyme activity on the cytoplasmic side of the membrane

Question 87

Hoe does the G-Protein Coupled receptor work?

Answer 87

Alpha has enzymatic activity to be able to exchange GDP for GTP And then this activated alpha GTP bound subunit will travel to adenylate cyclase Which then in turn uses ATP to activate cyclic AMP, activating protein kinase A Protein Kinase A (PKA), being a kinase, phosphorylates specific target proteins on serine or threonine residues, leading to changes in enzyme activity, gene expression, or cellular function depending on the cell type. Essentially, lipophobic molecules that cannot diffuse use this as a messenger to relay their messages. There are different pathways; Gs, Gi and Gq

Question 88

What does Gs do?

Answer 88

Activates adenylyl cyclase (an amplifier enzyme)→ ↑ cAMP → activates PKA (protein kinase A) → phosphorylation cascade which leads to a cellular response

Question 89

What does Gq do?

Answer 89

Activates phospholipase C → DAG (activates PKC) + IP3 (releases Ca²⁺ from ER). This is going to lead to the activation of phospholipase C, which is an amplifier enzyme in this specific signaling pathway The downstream signaling from here involved diacylglycerol (DAG) which stays in the plasma membrane, but in turn activates PKC (protein kinase C), which then phosphorylates downstream proteins Phospholipase C also activates inositol trisphosphate, which is going to go into the endoplasmic reticulum where it is going to release calcium Release of calcium can have a number of different responses

Question 90

What does Gi do?

Answer 90

Inhibits adenylyl cyclase → ↓ cAMP

Question 91

Why can epinephrine cause different effects in different tissues?

Answer 91

Different receptor isoforms (α vs β adrenergic receptors) activate different G proteins → different downstream responses. Ex. When epinephrine travels to the liver it releases glucose from the liver, which will provide an energy source to undergo a lot of the bodily reaction that you need in that fight or flight response

Question 92

Effect of epinephrine on intestinal blood vessels (α receptors)?

Answer 92

Vasoconstriction.

Question 93

Effect of epinephrine on skeletal muscle blood vessels (β receptors)?

Answer 93

Vasodilation.

Question 94

Fight-or-flight epinephrine responses?

Answer 94

Liver → glucose release. Heart → stronger/faster contractions. Fat → fatty acid release. Skeletal muscle vessels → dilation. Intestine/skin/kidney vessels → constriction.

Question 95

What are adrenergic receptors?

Answer 95

Adrenergic receptors (also called adrenoceptors) are G protein-coupled receptors (GPCRs) found on the surface of many cells in the body. They are activated by the catecholamines norepinephrine (noradrenaline) and epinephrine (adrenaline), which are hormones and neurotransmitters involved in the sympathetic nervous system—the system responsible for the "fight or flight" response.

Question 96

How can hormone signaling be turned off?

Answer 96

Hormone degradation. Receptor downregulation or desensitization. Breakdown of second messengers. Endocytosis of receptor-ligand complex. Negative feedback from biological effect.

Question 97

What happens when receptors are endocytosed?

Answer 97

clathrin-coated pits form and pinch off vesicles that will then be internalized inside the cell and hence trap the receptor inside it through endocytosis If the hormone is still bound to the receptor, then they can separate in the vesicles and the ligands can basically be degraded in the lysosome At this point the receptor has a few fates The cell may recycle it Will go back through the membrane via exocytosis, so that it can be bound by another ligand The cell may want it to stay in the vesicle