11. Endocrine System

Question 1

Endocrine System

Answer 1

• produces hormones that help maintain homeostasis and regulate reproduction and development

Question 2

Hormone

Answer 2

• chemical messenger produced in one part of the body that affects target cells in another part of the body

Question 3

General characteristics of hormones:

Answer 3

1. transported throughout the body in the blood
2. minute amounts can have significant influence on target cells
3. may be steroids, peptides, or modified amino acids

Question 4

Neurosecretory Cells

Answer 4

• special cells that link the hypothalamus and the pituitary gland, a gland attached to the base of the hypothalamus.
• neurosecretory cells are structured like neurons, but rather than secreting neurotransmitters into synapses that affect neighboring neurons, they secrete hormones into the blood.

Question 5

Two halves or lobes of pituitary:

Answer 5

1. Posterior pituitary. Two hormones produced by neurosecretory cells of hypothalamus and are stored here and released as needed —> ADH and oxytocin
2. Anterior pituitary. Releasing hormones are produced by neurosecretory cells in hypothalamus and secreted into the blood. This blood flows directly to the anterior pituitary where the releasing hormones stimulate the release of tropic hormones produced in the anterior pituitary. Tropic hormones are hormones whose target cells are other endocrine glands. Thus, they regulate hormone production by other glands.

Question 6

Hormones from………pituitary do not influence other glands, but target specific body tissues.

Answer 6

• posterior

- ADH and oxytocin

Question 7

Islets of Langerhans (regulation of blood glucose concentrations in blood by action of antagonistic hormones)

Answer 7

• bundles of cells among the cells of the pancreas
• contain two kinds of cells, alpha (a), and beta (b)

1. Beta cells secrete insulin. when conc of blood glucose rises (ex. after eating), beta cells secrete insulin into the blood. Insulin stimulates the liver and most other body cells to absorb glucose. Liver and muscle cells convert glucose to glycogen (for storage), and adipose cells convert glucose to fat. —> glucose conc decreases in the blood
2. Alpha cells secrete glucagon. When conc of blood glucose drops (ex. exercise), alpha cells secrete glucagon into the blood. Glucagon stimulates the liver to release glucose. The glucose in liver originates from breakdown of glycogen and conversion of amino acids and fatty acids into glucose.

Question 8

Antagonistic Hormones

Answer 8

• Insulin and Glucagon

Question 9

Antagonistic Hormones (another example)

Answer 9

• Parathyroid hormone (PTH) from the parathyroid glands increases Ca+2 in the blood by stimulating Ca+2 reabsorption in the kidney and Ca+2 release from bones.
• Calcitonin from the thyroid gland has the opposite effect on the bones and kidneys.

Question 10

Two methods by which hormones are known to trigger activities in target cells:

Answer 10

1. The hormone (usually a steroid) diffuses through the plasma membrane, through the cytoplasm, and into the nucleus. The hormone binds to a receptor protein in the nucleus -> receptor protein activates a portion of the DNA and turns on specific genes.
2. The hormone (usually a peptide) binds a receptor on the plasma membrane of the cell (receptor-mediated endocytosis). The receptor protein, in turn, stimulates production of one of the following second messengers:
   - Cyclic AMP (cAMP) is produced from ATP. cAMP triggers an enzyme that generates specific cellular chagnes.
   - Inositol triphosphate (IP3) is produced from membrane phospholipids. IP3 in turn, triggers the release of Ca+2 from the endoplasmic reticulum, which, in turn, activates enzymes that generate cellular changes.

Question 11

Posterior Pituitary Hormones

Answer 11

• ADH/vasopressin. Targets kidney. Increases reabsorption of H2O by increasing permeability of nephron’s collecting duct. Coffee blocks ADH.
• Oxytocin. Targets mammary glands. Stimulates release of milk. Secreted during childbirth, increases strength of uterine contractions.
• Both hormones produced by hypothalamus but stored in posterior pituitary.
• Posterior pituitary does not actually synthesize hormones.

Question 12

Anterior Pituitary Hormones (tropic hormones)

Answer 12

• FSH. Targets ovaries/tests. Regulates oogenesis and spermatogenesis. females: stimulates maturation of ovarian follicles. males: stimulates maturation of seminiferous tubules and sperm production.
• LH. Targets ovaries/testes. Regulates oogenesis and spermatogenesis. females: stimulate formation of corpus luteum. Males: stimulates interstitial cells of testes to produce testosterone.
• ACTH. Targets adrenal cortex. Secretion of glucocorticoids -> regulation of metabolism of glucose.
• TSH. Targets thyroid. Secretion of T4 and T3

Question 13

Anterior Pituitary Hormones (not tropic hormones) (direct hormones)

Answer 13

• PRL. Targets mammary glands. Production of milk

- GH. Targets bone, muscle. Stimulates growth. AKA somatotropin.

Question 14

Pancreas (alpha cells)

Answer 14

• Glucagon. Targets liver. Increases blood glucose

Question 15

Pancreas (beta cells)

Answer 15

• Insulin. Targets liver, muscles, fat. Lowers blood glucose.

Question 16

Adrenal Gland (medulla)

Answer 16

• Epinephrine (adrenaline) and norepinephrine (noradrenalin). Targets blood vessels, liver and heart. Increases blood glucose, constricts blood vessels (fight or flight response)

Question 17

Adrenal Gland (Cortex)

Answer 17

• Glucocorticoids (cortisol), mineralcorticoids (aldosterone). Targets general/kidney. Increases blood glucose (glucocorticoids), inreases reabsorption of Na+ and excretion of K+ (aldosterone)

Question 18

Thyroid

Answer 18

• T4 (thyroxin) and T3 (triiodothyronine), calcitonin. Targets general, bone. Increases cellular metabolism, lowers blood Ca+2.

Question 19

Parathyroid

Answer 19

• PTH (parathyroid hormone). Targets bone. Increases blood Ca+2.

Question 20

Testis

Answer 20

• Testosterone. Spermatogenesis, secondary sex characteristics.

Question 21

Ovary

Answer 21

• Estrogen. Uterus/general. Menstrual cycle, secondary sex characteristics.
• Progesteron. Uterus. Menstrual cycle, pregnancy.

Question 22

Pineal

Answer 22

• Melatonin. Target body. Circadian rhythms.

Question 23

Endocrine vs. Exocrine

Answer 23

• Endocrine synthesize and secretes hormones into bloodstream.
• Exocrine secrete substances into ducts (ex. gall bladder.
• Pancreas is both endocrine and exocrine

Question 24

Paracrine

Answer 24

• cell signaling where target is nearby

Question 25

Autocrine

Answer 25

• cell signaling via hormone/chemical messenger that binds to receptor on same cell

Question 26

Prostaglandins

Answer 26

• locally acting autocrine/paracrine lipid messenger molecules that have physiological effect (contract/relax smooth muscle).

Question 27

Hormone Types:

Answer 27

1. Peptide. synthesized in rough ER and modified in Golgi (requires vesicle to cross membrane), acts on surface receptors via second messengers (cAMP, IP3)
   Receptor-mediated endocytosis -> protein stimulates production of second messenger. All pituitary hormones, PTH (parathyroid), glucagon and insulin.
2. Steroid. synthesized from cholesterol in smooth ER. Direct stimulation: “steroid” diffused past plasma membrane and binds receptor in cytoplasm -> hormone + receptor transported to nucleus -> binds activate portion of DNA. Includes glucocorticoids and mineralcorticoids of adrenal cortex: cortisol & aldosterone; gonadal hormones: estrogen, progesteron, and testosterone.
3. Tyrosine Derivatives. Formed by enzymes in cytosol or on rough ER. Thyroid hormones: lipid soluble; require protein carrier in blood; bind to receptors in nucleus. Catecholamines (epi and norepi); dissolve in blood; bind to receptors on target tissue and mainly act via second messengers. Includes thyroid hormones (T3 and T4 aka thyroxine) and catecholamines formed in adrenal medulla (epi and norep)

Question 28

Tropic Hormones

Answer 28

• stimulate other endocrine glands.

Question 29

Thyroid

Answer 29

• located on ventral surface of trachea
• Thyroxine (T4) and Triiodothyronine (T3): derived from tyrosine and necessary for growth and increase basal metabolic rate in body (negative feedback on TSH). Hypothyroidism (undersecretion) —> low heart rate and respiratory rate. Hyperthyroidism (oversecretion) —-> increased metabolic rate and sweating. Both lead to GOITERS.
• Calcitonin (“tone down” Ca+2) in blood. decrease plasma Ca+2 by inhibiting its release from bone. Decrease osteoclast activity and number.

Question 30

Disorders of Thyroid

Answer 30

• Anchondroplasia (AD): dwarfism –> more common

- Progeria (AR); premature aging —–> less common

Question 31

Parathyroid

Answer 31

• four pea-shaped structures attached to back of thyroid.
• Parathyroid hormone (PTH) antagonistic to calcitonin. Raises Ca+2 conc in blood by stimulating release from bone. Increases Osteoclast proliferation. Increases renal Ca reabsorption.

Question 32

Thymus

Answer 32

• involved in immune response
• secretes thymosins that stimulate lymphocytes (WBCs) to become T-cells (identification and destroying of infected body cells)

Question 33

Adrenal Gland

Answer 33

• on top of kidneys:
• Adrenal Cortex. secretes only steroid hormones. Glucocorticoids (cortisol and cortisone), raise blood glucose levels; stress hormones. Mineralcorticoids (aldosterone) increases reabsorption of Na+ and excretion of K+, causes passive reabsorption of water in nephron -> rise in blood volume/pressure. Cortical sex hormones (androgens = male sex hormones)
• Adrenal Medulla. Epinephrine and Norepinephrine (adrenaline and noradrenaline). “fight or flight”. catecholamines. “fight or flight” (sympathetic N.S.): considered stress hormones. Glycogen -> glucose, vasoconstrictor to internal organs + skin but vasodilator to skeletal muscle, increased heartbeat.

Question 34

Somatostatin

Answer 34

• released by delta cells of pancreas; inhibits both insulin and glucagon; possibly increases nutrient absorption time.

Question 35

Gastrointestinal Hormones

Answer 35

• Gastrin: food in stomach, stimulates secretion of HCL
• Secretin: small intestine, acidic food enters from stomach –> neutralize acidity of chyme by secretion of alkaline bicarbonate.
• Cholecystokinin: small intestine, presence of fat—> contraction of gall bladder and release of bile (emulsify fat)