Lecture Three: Endocrine Tissues

Question 1

Describe the structure of the pituitary gland;

Answer 1

The pituitary gland is connected to the hypothalamus by the infundibulum. (third ventricle is located superiorly)

The pituitary gland is situated in the sphenoid bone

The pituitary gland is divided into;

Posterior pituitary; Neural extension

Anterior pituitary; True endocrine gland of epithelial origin.

Look at the diagram if needed

Question 2

How can the anterior pituitary be further divided?

Answer 2

Anterior pituitary;

Pars distalis (large most anterior portion)
Pars intermedia
Pars tubercle (surrounds posterior pituitary extension, forming the infundibulum)

Question 3

Write some notes on the anterior pituitary;

Answer 3

Contains endocrine cells that synthesise and secrete seven hormones;

Pars Distalis;

• Prolactin
• TSH
• ACTH
• GH
• FSH
• LH

Pars intermedia
- MSH

Question 4

Describe how the hypothalamus - pituitary neuroendocrine organ functions

Answer 4

The hypothalamus synthesizes and secretes regulatory hormones which inhibit or release hormones from the anterior pituitary.

The posterior pituitary is a neural extension containing neurosecretory neurons that upon depolarisation released their stores of ADH or oxytocin

Question 5

List the regulatory hormones synthesised by the hypothalamus:

Answer 5

PRH -> Prolactin
Dopamine / PIH -> inhibits prolactin
TRH -> TSH and prolactin
CRH -> ACTH
GHRH -> GH
GHIH -> inhibits GH
GNRH -> FSH and LH

Question 6

What endocrine glands do the hormones from the anterior pituitary act on?

Answer 6

Prolactin (effector = breast tissue)
TSH -> Thyroid Gland
ACTH -> Adrenal cortex
GH -> Liver
FSH and LH -> endocrine cells

These all produce further hormones that act on many tissues (except prolactin)

Question 7

Write some notes on the pars intermedia;

Answer 7

Contains special endocrine cells that secrete only MSH but has a wide range of functions

Question 8

Write some notes on the hypothalamic hypophyseal portal system;

Answer 8

The superior hypophyseal artery supplies blood to the capillary bed covering the hypothalamus.

This feeds via portal vessels to the capillary bed covering the anterior pituitary. These carry trophic hormones from the hypothalamus directly to the AP. This capillary bed drains into the veins.

The inferior hypophyseal artery feeds into the capillary bed covering the posterior pituitary. Neurosecretory neurons can release their hormones into these vessels.

Question 9

Whats the function of the hypophyseal portal system other than carrying hormones away?

Answer 9

It allows hyothalamic hormones to travel a short distance rather than circulating the body. EFFICIENT

Question 10

Describe the adrenal gland and function;

Answer 10

Adrenal medulla - Secretes catecholamines

Adrenal cortex

• Zona reticularis (7% vol), Secretes sex hormones
• Zona fasiculata, Secretes glucocorticoids i.e cortisol
• Zona Glomerulosa (15% vol), Secretes Mineral corticoids

Question 11

Describe the HPA pathway for control of cortisol secretion;

Answer 11

“The stress response” - Endocrine reflex?

Circadian rhythm and Stress influence the hypothalamic release of CRH

CRH -> ACTH -> Cortisol

Acts on;

• Immune system -> Function supressed
• Liver -> Gluconeogenesis
• Muscle -> Protein Catabolism
• Adipose Tissue -> Lipolysis

Negative feedback

Cortisol (long loop negative) Therefore acts on AP and Hyp

ACTH (short loop negative) Acts on Hyp

Question 12

Where is the thyroid gland located?

Answer 12

Inferior to the larynx and is a butterfly shape.

Question 13

Describe a cross section of the thyroid gland;

Answer 13

Contains follicles which stored hormones

Follicle is formed by a peripheral ring of follicle cells that secrete T3 and T4

Follicle is filled with colloid that is a glycoprotein

Attached to some follicles is C cells that secrete calcitonin

Capillaries and outer fibrous capsule

Question 14

Describe thyroid hormone synthesis;

Answer 14

1) Follicular cells synthesise enzymes and thyroglobulin for colloid
2) Iodine is (actively) co-transported into the cell with Na and transported into the colloid
3) Enzymes add iodine to thyroglobulin to make T3 and T4
4) Thyroglobulin is taken back into the cell
5) Intracellular enzymes seperate T3 and T4 from the protein
6) Free t3 and T4 enter the circulation

Question 15

What are parathyroid glands?

Answer 15

Glands located at the posterior of the thyroid and there are four of them.

Question 16

What are parathyroid hormones important in?

Answer 16

Secrete parathyroid hormones that are important for regulating Ca levels and bone health

Question 17

Describe the pathway of thyroid hormones control;

Answer 17

Tonic release of TRH from hyp

TRH -> TSH -> T4, T3 Systemic effects

Long loop negative feedback

Question 18

Describe the endocrine cells of the pancreas;

Answer 18

1% of pancreatic cells are endocrine. 99% are enzymes, other exocrine functions

Endocrine cells (in islets of langerhans) include

• Alpha cells, secretes glucagon
• Beta cells, secretes insulin, amylin
• D cells secrete Samatostatin
• F cell, secretes pancreatic polypeptide

Question 19

Describe The insulin glucagon balance and function;

Answer 19

Fed state; Insulin dominates =

• Inc glucose oxidation
• Inc glycogen synthesis
• Inc fat synthesis
• Inc protein synthesis

Fasted state; Glucagon dominates

• Inc glycogenolysis
• Inc Gluconeogenesis
• Inc ketogenesis

Question 20

Describe the feedback loop for steroid hormones

Answer 20

GnRH -> LH and FSH -> Steroid hormones and gamete production

Long loop Negative and Positive at Ant P and Hyp levels.

LH and FSH short loop negative

Question 21

Write notes on HPA integration of nervous and endocrine systems

Answer 21

The hypothalamic-pituitary-adrenal (HPA) pathway controls cortisol secretion.

Cortisol secretion is continuous and it has a strong diurnal pattern and it increases with stress.

CRH -> ACTH -> Cortisol

Cortisol acts as a negative feedback signal, inhibiting ACTH and CRH secretion.