5. Endocrine Glands

Question 1

Hypothalamus and the Pituitary Gland Diagram

Answer 1

Question 2

Hypothalamus and the Pituitary Gland

Answer 2

• anterior pituitary is glandular epithelial tissue - adenohypophysis
• posterior pituitary is composed of nervous tissue - neurohypophysis
• the release of hormones from both anterior and posterior pituitary controlled by the hypothalamus

Question 3

Posterior Pituitary

-simpler of the two

Answer 3

• along w hypothalamus forms the neuroendocrine system - does not produce hormones
• stores and releases 2 small peptide hormones (made in hypothalamus)
  
  • vasopressin - conserves water during urine formation
  • [not relevant] oxytocin - stimulates uterine contraction during childbirth and milk ejection during breast-feeding

Question 4

Anterior pituitary

Answer 4

• epithelial tissue (endocrine? tissue?)
• hormones are made/synthesises and released into the circulatory system
• 6 major tropic hormones

Question 5

anterior pituitary hormones

Answer 5

• growth hormone - GH
• thyroid stimulating hormone - TSH
• adrenocorticotropic hormone - ACTH
• follicle-stimulating hormone - FSH - [not relevant]
• Luteinising hormone - LH [not relevant]
• Prolactin - PRL [not relevant]

Question 6

tropic hormones

Answer 6

hormones that control release of other hormones - cascade

Question 7

Regulation Of Anterior Pituitary Hormone Secretion

Answer 7

• not constant

2 factors for anterior pituitary hormone secretion

1. hypothalamic hormones
2. feedback by target-gland hormones

Question 8

the hypothalamic hormones - 7

Answer 8

“Tropic hormone for tropic hormones”

e.g. Hypothalamus gland tells pituitary to secrete TSH for thyroid

TSH (thyrotropin) is tropic hormone for thyroid

• The secretion of anterior pituitary hormones is stimulated or inhibited by one or more of the seven hypothalamic hormones.
• These are small peptide hormones that are synthesized in the hypothalamus.
• Either inhibiting or releasing hormones.

Question 9

Negative feedback control

Answer 9

3 integrating centres

1. hypothalamus
2. pituitary gland
3. endocrine gland

hormones themselves are the negative feedback signal

example right is for the release of cortisol

Question 10

The hypothalamic-hypophyseal portal system

Answer 10

Question 11

Growth Hormone

Answer 11

• stimulate growth and cell reproduction
• synthesised, stored and secreted by the anterior pituitary gland

Question 12

Control of GH

Answer 12

The synthesis and secretion of GH is regulated mainly by:

1. GHRH
2. GHIH (Somatostatins)
3. Insulin-like growth factors (IGF-1) via negative feedback loop

-reminder it is a tropic hormone and IGF-1 actually targets cells with growth

Question 13

Endocrine control of growth

Answer 13

• growth depends on growth hormone but is influenced by other factors

– Genetic determination of an individual’s maximum growth capacity

– An adequate diet

– Freedom from chronic disease and stressful environmental conditions

– Normal levels of growth-influencing hormones (Growth Hormone, sex hormones, thyroid hormone, insulin)

Question 13

Normal growth curve

Answer 13

• Rate of growth is not continuous
• Factors responsible for growth are not the same throughout the growth period

Three growth periods:

1. Fetal - GH does not play a role
2. Postnatal - 2 years old to puberty
3. Puberty

Question 14

GH Growth Promoting Activity

Answer 14

• GH stimulates growth of both soft tissues and the skeleton.

1. Increasing the number of cells (hyperplasia)
2. Preventing apoptosis (programmed cell death)
3. Increasing the size of cells (hypertrophy) by promoting the uptake of amino acids (raw materials for protein synthesis) and stimulating protein synthesis
4. Inhibits protein degradation

• Stimulates the growth of long bones (skeleton) resulting in increased height (most dramatic effect of GH).

Question 15

GH Growth Promoting Activity (Part 2)

Answer 15

GH itself does not act directly on its target cells to bring about growth producing actions.

Growth promoting activity of GH occurs via peptide mediators, known as insulin-like growth factors (IGF-1)

Question 16

Metabolic effects of GH

Answer 16

major metabolic role of GH

• promote mobilisation of fat stores as major energy source
• conserve glucose for glucose dependent tissues like the brain

maintains the body during prolonged fasting or other situations when the body’s energy needs exceed available stores

1. Increased rate of protein synthesis in all body cells
2. Increased fatty acid mobilization from adipose tissue.
3. Increased fatty acid use by body tissues.
4. Decreased rate of glucose/glycogen use by body tissues.

Question 17

Growth Hormone Deficiency

Answer 17

• Due to pituitary defect or hypothalamic dysfunction
• Hyposecretion of GH in child is one cause of dwarfism
• Deficiency in adults produces relatively few symptoms

Question 18

Growth Hormone Excess

Answer 18

• Most often caused by tumor of GH-producing cells of anterior pituitary
• Symptoms depend on age of individual when abnormal secretion begins
  
  • Gigantism – cause by overproduction of GH in childhood before epiphyseal plates close
  • Acromegaly – occurs when GH hypersecretion occurs after adolescence

Question 19

Other hormones essential for normal growth

Answer 19

Other hormones are essential for normal growth

– Thyroid hormone
• Growth severely stunted in hypothyroid children • Hypersecretion does not cause excessive growth

– Insulin
• Deficiency often blocks growth
• Hyperinsulinism often spurs excessive growth

– Androgens
• Pubertal growth spurt, stimulate protein synthesis in many organs
• Effects depend on presence of GH

– Estrogens

• Effects of estrogen on growth prior to bone maturation are not well understood

Question 20

Pineal Gland Functions

Answer 20

• helps keep body’s circadian rhythms in synchrony with light-dark cycle
• promotes sleep
• influences reproductive activity, including puberty
• acts as antioxidant to remove free radicals
• enhances immunity