Endocrine glands
Functions:
1. Differentiates: Reproductive and nervous systems in the developing fetus
- Stimulates: Sequential growth and development during childhood and adolescence
- Coordinates: Male and female reproductive systems
- Maintains: Optimal internal environment
- Initiates: Corrective and adaptive responses when emergency demands occur
Hormones
Chemical messengers/communicators
Types of hormones:
- Autocrine: self-stimulate
- Paracrine: local cells
- Endocrine: remote cells
General characteristics:
- Inactivated by the liver or directly excreted by the kidneys
- Operate within mostly negative feedback systems
- Specific rates and rhythms of secretion
- Affect only target cells with appropriate receptors
Regulation of hormone release
Maintain a regulated level of certain substances/other hormones in response to an alteration in the cellular environment
Influenced by:
- Internal chemical environment
- Current growth/metabolic needs
- Neural factors
Hormone transport
- Water-soluble hormones: attach to EXTRACELLULAR cell membrane receptors (d/t their high molecular weight); circulate freely in blood
- Lipid-soluble hormones: easily diffuse across the cell membrane and attach to INTRACELLULAR receptors; typically require transporter/carrier protein in blood
Hormone receptors
Target cells: recognize and bind with a high affinity to hormones to initiate a signal (increased hormone receptors = increased sensitivity)
Regulations:
1. Up-regulation: increase in the number of cellular receptors in response to LOW concentration of hormones
- Down-regulation: decrease in the number of cellular receptors in response to HIGH concentration of hormones
Positive feedback loops
Far less common, self-perpetuating; the stimulus is promoted rather than suppressed
i.e. The release of oxytocin from the posterior pituitary gland during labor; breast milk production
Hypothalamus and pituitary gland
Located at the base of the brain
Integrates the neuro and endocrine systems
Produce: (1) Releasing-, (2) inhibitory-; and (3) tropic-hormones
Hypothalamus
Functions:
1. Hormone monitoring (production and release) by (1) stimulating the autonomic nerves and (2) by releasing hormones from the pituitary gland
- Regulate body temp.
- Maintain daily physiological cycles
- Other: Control appetite, manage sexual behavior, and regulate emotional responses
Hormones: PRH, PIF, TRH GnRH, substance P, GRF (GH-releasing factor), somatostatin (GH-inhibiting factor), CRH (corticotrophin-releasing hormone)
Hormones of the pituitary gland
ANTERIOR Pituitary:
- Corticotropin-related hormones: ACTH and MSH
- Glycoproteins: TSH, FSH, and LH
- Somatomammotropins: Somatotropin (GH) and prolactin
- Minor corticotropins: Beta-lipoproteins (fat catabolism) and beta-endorphins (pain perception)
POSTERIOR Pituitary: Stores and secretes hormones synthesized in the hypothalamus; (1) ADH and (2) Oxytocin
Adrenal glands
Two pyramid-shaped organs above the kidneys
Consist of the adrenal cortex (outer portion) and adrenal medulla (inner portion)
Adrenal cortex hormone #1: Cortisol, cortisone, and corticosterone (Glucocorticoids)
Functions:
- Controls use of fats, proteins, and carbs.
- Suppresses inflammation
- Regulates BP
- Increases blood sugar
- Decreases bone formation
- Controls sleep/wake cycle (diurnal rhythms)
HPA axis
Stress response pathology:
- Hypothalamus releases CRH (in response to low cortisol)
- Anterior pituitary produces and releases ACTH into the bloodstream
- Adrenal gland produces and releases cortisol (cortex) and epinephrine (medulla)
- Increased cortisol and epinephrine
- Hypothalamus stops producing CRH
Adrenal cortex hormone #2: Aldosterone (Mineralcorticoid)
Pathway:
- Low BP/ECF/serum Na+ or High urine Na+/serum K+
- Angiotensinogen (liver) and renin (kidneys) form angiotensin I
- Angiotensin I is converted to angiotensin II by ACE (lungs)
- Angiotensin II causes (1) arteriole vasoconstriction and (2) stimulates production and release of aldosterone (adrenal cortex)
- Aldosterone causes (1) Na+ and water retention (and K+ excretion), and (2) stimulation and release of ADH (posterior pituitary), which further increases ECF and BP
Adrenal cortex hormone #3: Precursor sex hormone (Androgenic steroids)
Secreted in response to ACTH from the anterior pituitary
Precursor sex hormone is converted to:
- Estrogen (in ovaries)
- Testosterone (in testes)
Adrenal medulla hormones: Epinephrine, norepinephrine (Catecholamines)
Stimulated upon physical and emotional stress responses (“fight or flight”)
Receptors:
- Alpha: found only in the arteries
- Beta: found in heart, lungs, arteries of skeletal muscles
Effects:
- Increase blood sugar, HR, contractility, and metabolic rate
- Bronchodilation (increases oxygen supply)
- Breakdown of fat in cells
- Pupil dilation
- Vasoconstriction
Thyroid gland
Stimulated by TRH (hypothalamus) and TSH (anterior pituitary) via negative feedback loop
Hormones:
1. CALCITONIN: Decreases serum Ca2+ by INHIBITING (1) osteoclast activity and (2) Ca2+ reabsorption in kidneys
- T3 and T4: Regulate vital bodily functions (such as metabolism, CO, HR, rate of ventilation, modulating SNS activity, brain development, and endometrial thickening)
Parathyroid glands and parathyroid hormone (PTH)
PTH: Increases serum Ca2+ by PROMOTING (1) osteoclast activity and (2) Ca2+ reabsorption in kidneys; and (3) co-factors with vitamin D to further increase Ca2+ absorption in the intestines
PTH also increases phosphate excretion via urine
Pancreas
Produces digestive enzymes and hormones
Types of cells and hormones:
1. ALPHA cells: Glucagon (increases BG levels)
- BETA cells: Insulin (mobilizes glucose into cells) and amylin (co-secreted with insulin to inhibit glucagon secretion, delay gastric emptying, and acts as a satiety agent)
- DELTA cells: Somatostatin (GH-inhibiting) and gastrin (stimulates production and secretion of stomach acid)
Insulin
Regulated by chemical, hormonal, and neural mechanisms; and promoted by increased BG
Facilitates uptake of (1) glucose and (2) K+ into cells
