Chapter 16 Endocrine & Neuroendocrine Physiology

Question 1

Endocrine Glands

• A.A. Berthold speculated that the testes of a rooster secreted something that was responsible for its male characteristics in 1849
• In 1905, Starling described 3 characteristic properties of hormones:

1. Hormones are synthesized by specific tissues or glands
2. Hormones are secreted into the bloodstream, which carries them to their site(s) of action
3. Hormones change the activities of target tissues or organs

Answer 1

Question 2

Endocrine Glands: Hormone Structure

• There are 3 criteria determining if a tissue has endocrine function:

1. Removal of the tissue produces a deficiency syndrome
2. Replacement of the removed tissue reverses the deficiency syndrome
3. Injection of the putative hormone should also relieve deficiency symptoms

Answer 2

• Hormones belong to 4 structural classes:
  1. Amines
• Catecholamines & Thyroid Hormone
  2. Steroid hormones
  3. Peptide hormones
  4. Eicosanoids

Question 3

Amines

Catecholamines

• Made from tyrosine
• Water soluble
• Stored in chromaffin granules
• Interact with binding proteins in plasma
• Receptors on cell membrane
• Secreted from adrenal medulla

Answer 3

Thyroid Hormone

• Iodinated tyrosine
• Fat soluble
• Stored in colloid
• Interact with binding proteins in plasma
• Intracellular receptors
• Secreted from thyroid gland

Question 4

Steroid Hormones

• Made from cholesterol
• Fat soluble
• Not stored
• Interacts with binding proteins in plasma
• Intracellular receptors (most)
• Secreted from adrenal cortex, gonads, placenta

Answer 4

Question 5

Steroid & Lipophilic Hormones

Answer 5

Question 6

Peptide Hormones

• Made from amino acids
• Water soluble
• Made in RER
• Stored in secretory granules
• Transported as free hormone
• Extracellular receptors
• Many secretion sites

Answer 6

Question 7

Hormone Effectiveness

• Several things alter hormone effectiveness
• Amount of free hormone
  
  • Rate of synthesis
  • Rate of secretion
  • Concentration of binding proteins
  • Dilution of hormone in plasma
• Number of receptors

Question 8

Endocrine Glands: Negative-Feedback Loops

• The endocrine system runs on negative-feedback systems:
  
  • Short-loop feedback: the response of the target tissue (1) feeds back to the endocrine tissue
  • Long-loop feedback: secondary targets (2) feed back to the endocrine tissue

Answer 8

Question 9

Posterior Pituitary and Hormones

Answer 9

Question 10

Anterior Pituitary & Hormones

Answer 10

Question 11

Growth Hormone (somatotropin)

• Effects depend on age
• Triglyceride catabolism
• GH induces the liver to produce insulin-like growth factors (IGF-1) which further promote tissue growth
• Increases cell size (hypertrophy) and cell number (hyperplasia)
• Bone growth (thickness & length)
• Cartilage is a primary target tissue for GH resulting in bone growth; growth hormone and thyroxine are synergistic hormones in development
• In adults, GH effects are similar to those of glucagon (these effects also occur in immature animals)

Answer 11

Question 12

Prolactin

• Causes milk production (lactogenesis)
• Stimulates crop milk
• Reproductive behaviors (incubation behavior)
• Brood patch
• Osmoregulation
• Control differs in mammals & birds

Question 13

Thyroid Hormone

• Thyroxine causes increased metabolism in skeletal and cardiac muscle, the liver, and the kidney; this causes the metabolic production of heat.
• T4 is most abundant, T3 is most active
• Increases response to catecholamines (from sympathetic system)
• Increases heart rate
• Acts permissively with GH
• Controls metamorphosis

Answer 13

Question 14

The HPA Axis

Answer 14

Question 15

Catecholamines

The adrenal medulla is physiologically equivalent to a giant postganglionic sympathetic neuron which releases epinephrine &/or norepinephrine into the circulation

Answer 15

Question 16

Stress

Answer 16

Question 17

Antidiuretic hormone (ADH)

• Vasopressin
  
  • Stimulated by hypothalamic osmoreceptors
  • Pressor effect
  • Antidiuretic effect
• Arginine Vasotocin
  
  • Lower vertebrates
  • Oviposition in birds
  • Stimulates ACTH-induced steroidogenesis in tadpoles

Answer 17

Question 18

Calcitonin and Parathyroid Hormone Effects

Calcitonin and parathyroid hormone have opposing effects on blood Ca2+ levels

Answer 18

Question 19

Mammalian Hormones Involved in Water and Electrolyte Balance

Answer 19

Question 20

Insulin

Answer 20

Insulin & Glucagon

Question 21

Insulin, Glucogon, & Steak

Answer 21

Question 22

Prostaglandins

• Prostaglandins are arachidonic acid-derived substances which tend to have paracrine as well as endocrine effects that are short-lived unlike other lipid-soluble hormones
• Prostaglandins have varied effects including mediating the inflammatory response

Answer 22

Question 23

Invertebrate Endocrinology

• Mollusks
  
  • Juxtaganglionar organ secretes peptides into hemolymph during egg laying
  • Bag cells secrete egg-laying hormone (ELH)
• Annelids
  
  • Annetocin causes egg-laying behavior
• Crustaceans
  
  • X-organ (in eyestalks)
    
    • Chromatophorotropins: change color of cuticle
    • Crustacean hyperglycemic hormone: releases glucose and glycogen from hepatopancreas
    • Vitellogenesis-inhibiting hormone: inhibits egg production
• Y-organ (in head)
  
  • Crustecydsone: causes molting

Question 24

Insect Hormones

• Prothoracicotropic hormone (PTTH) is made in the brain.
  
  • Neurohormone
  • Released into circulation at corpora cardiaca and corpora allata
  • Travels through hemolymph to prothoracic glands
• Prothoracic gland
  
  • At back of head or thorax
    
    • Secretes ecdysone
    • A steroid (ecdysteroid)
  • Induces molting: Replacing exoskeleton with another
  • Ecdysis: Removal of old exoskeleton

Answer 24

• Corpora allata
  
  • Behind brain
  • Secretes juvenile hormone (JH)
• Bursicon
  
  • Neurohormone
  • Cuticle development after molting
• Eclosion hormone
  
  • Neurohormone
  • Emergence from pupa

Question 25

Insect Hormones prt2

• Juvenile Hormone
  
  • Released from corpora allata
  • Inhibited by allostatin
  • Stimulated by allotropin
• Molting:
  
  • No JH: Ecdysone causes metamorphosis to adult
  • With JH: Ecdysone causes molting, but not metamorphosis

Answer 25