6. Endocrine Tissues

Question 1

Give some examples of organs that contain endocrine cells and tissues.

Answer 1

Thymus, heart, liver, stomach, kidney, ovaries, testes.

Question 2

Where is the pituitary gland located and what does it secrete?

Answer 2

Base of the brain.
Anterior - thyroid stimulating, adrenocorticotropics, FSH, LH, GH, prolactin.
Posterior - antidiuretic hormone/vasopressin, oxytocin

Question 3

Where is the thyroid gland and what does it secrete?

Answer 3

Anterior to the trachea, in two lobes joined by ismus

Thyroxine T4, triiodothyronine T3

Question 4

Where is the parathyroid gland and what does it secrete?

Answer 4

Lies on the dorsal surface of thyroid gland
4 glands - 2 pairs
Secretes para-thyroid hormone

Question 5

Where are the adrenal glands located and what do they secrete?

Answer 5

Top of each kidney, two sections; medulla inner and cortex outer surrounding medulla.
Cortex secretes corticosteroids, steroid hormones.
Medulla - chromaffin cells, release of adrenaline and noradrenaline.

Question 6

Where is the pancreas and what does it secrete?

Answer 6

Left of and behind the stomach, is both an exocrine and endocrine gland.
Exocrine secretes digestive enzymes into duodenum.
Endocrine has islets of Langerhans:
- Alpha - glucagons
- Beta - insulin

Question 7

What endocrine hormones affect the heart?

Produced from the heart as can be an endocrine organ

Answer 7

Atrial natriuretic factors act on kidneys.
Relaxes arterioles inhibits renin and aldosterone
Prevents sodium reabsorption by kidney, less salt

Question 8

What endocrine hormones does the stomach produce?

Answer 8

Gastrin stimulates gastric acid secretion
Ghrelin and leptin appetite control
Somatostatin inhibits secretion of hormones
Secretin stimulates secretion of water and bicarbonate

Question 9

What endocrine hormones does the liver produce?

Answer 9

Insulin-like growth factor mediates GH dependent growth
Angiotensinogen precursor for angiotensin
Angiotensin increases blood pressure, vasoconstrictor
Thrombopoietin regulates production of platelets

Question 10

What endocrine hormones does the duodenum produce?

Answer 10

Secretin stimulates of water and bicarbonate

Cholecystokinin stimulates pancreatic enzymes

Question 11

What endococrine hormones does the kidney produce?

Answer 11

Renin converts angiotensin 1 to 2
Erythropoietin produces RBCs by bone marrow
Calcitriol promotes calcium absorption
Thrombopoietin regulates production of platelets

Question 12

What are peptide hormones?

Describe their characteristics.

Answer 12

Glycoproteins, e.g. insulin, glucagon, prolactin, PTH
Made in advance and stored in secretory vesicles.
Dissolved in the plasma, receptors on membranes.
Activates second messenger systems.

Question 13

What are steroid hormones?

Describe their characteristics.

Answer 13

Synthesised on demand from precursors.
Bound to carrier proteins as lipophilic.
Receptors within nucleus or cytoplasm.
Activation of genes for transcription.
e.g. oestrogen, androgens, aldosterine, cortisol

Question 14

What are catecholamines?

Describe their characteristics.

Answer 14

Made in advance stored in secretory vesicles.
Dissolved in plasma, attach to receptors on membrane.
Activate second messenger systems.
e.g. adrenaline, noradrenaline, also dopamine

Question 15

What are thyroid hormones?

Describe their characteristics.

Answer 15

Made in advance as precursors, stored in vesicles.
Bound to carrier proteins, receptors on nucleus.
Activates genes for transcription and translation.
Thyroxine T4 and triiodothyronine T3.

Question 16

What are lipid hormones?

Answer 16

Endocannabinoids are lipid neurotransmitters, can bind to cannbinoid receptors.
Anandimide acts on cannabinoid receptors throughout the body controlling pain.

Question 17

What can the hypothalamus control?

Answer 17

Thermoregulation
Plasma osmolality
Heart rate and blood pressure
Feeding, circadian rhythms, emotion, sexual behaviour
Lactation, stimuli from autonomic nervous system

Question 18

What does the hypothalamus produce?

Answer 18

Vasopressin (ADH) and oxytocin

Six hormones that travel via the hypothalamo-hypophyseal portal system to anterior pituitary.

Question 19

Describe the structure of the pituitary gland

Also known as the hypophysis

Answer 19

Divided into two lobes, anterior and posterior joined by stalk known as infundibulum.

Question 20

What is a portal system?

Answer 20

Differ from typical circulatory route, blood passes through two sets of smaller vessels before returning to the heart.
Blood collects in portal vessels/veins then brancing into capillary network to second location before branching to heart.

Question 21

What are two examples of a portal system?

Answer 21

Hypothalamo-hypophyseal portal system

Hepatic portal vein

Question 22

Outline the development of the endocrine system?

Answer 22

From 5 weeks onwards.
1. Pituitary develops from neurohypophyseal bud and hypophyseal pouch (Rathke’s pouch)
2. Thyroid develops from 2nd pouch in pharynx
3. Parathyroid and thymus develop from 3rd/4th
4. Pancrease from foregut
5. Adrenals develops from intermediate mesoderm and neural crest, in centre of foetus
Takes 8-12 weeks to develop pituitary
Bud grows around mouth and Rathke’s pouch
Infundibulum grows around pouch pressing it, closes around mouth - pars intermedia cavity.

Question 23

Describe the main pathways within the posterior pituitary.

Answer 23

ADH affects kidneys.
Oxytocin - males, smooth muscle in prostate
In females, uterine smooth muscle, mammary glands.

Question 24

Describe the pathways for LH and FSH.

Answer 24

LH and FSH produced by anterior pituitary.
LH - ovaries to produce oestrogen, progestrone
- Testes to produces inhibin and testosterone.
Same for FSH.

Question 25

Describe some of the other pathways for the anterior pituitary lobe.

Answer 25

ACTH direct control by nervous system overrides, autonomic nervous system. TSH to thyroid gland for T3 T4 release. GH to liver to somatmedins to bone, muscle, tissue. MSH melanocytes, make melanin.

Question 26

How are pituitary hormones controlled?

Answer 26

All subject to constitutive and regulated merocrine secretion, hence why there is always a small concentration of these hormones in the blood.

Question 27

Describe the levels of thyroid hormones in hypothyroidism and hyperthyroidism.

Answer 27

Hyperthyroidism - low TSH, high T3 and T4 Overactive production of T3/T4 but feedback to TSH. Hypothyroidism - high TSH, low T3/T4 If there are low levels of T3/T4 will feed back to hypothalamus and pituitary for higher levels TSH.

Question 28

What is Hashimoto's?

Answer 28

High TSH, low T3 and T4 Thyroiditis, hypothyroidism. Autoimmune disease that gradually destroys thyroid gland, fatigue, weight gain, muscle pain.

Question 29

What is Grave's disease?

Answer 29

TSI antibodies cause increases in T3 and T4 as act like TSH. Hence low levels of TSH.

Question 30

What are parafollicular cells?

Answer 30

Neuroendocrine cells that migrate into the thyroid during thyroid development in the embryo. Produce calcitonin, independent of thryoid hormone synthesis. Inhibits osteoclast activity and renal calcium and phosphate reabsorption.

Question 31

What is the parathyroid gland?

Answer 31

Makes PTH to increase plasma calcium levels, causes bone to release more calcium. Calcium is essential in nerve conduction and muscle contraction.

Question 32

Describe the characteritics of the adrenal medulla.

Answer 32

Composed of chromaffin cells, modified neurons. | Myelinated presynaptic sympathetic nerve fibres pass through these cells. Cause release of products.

Question 33

Describe the structure of the adrenal cortex.

Answer 33

``` Three layers: - Outer zone glomerulosa, aldosterone - Middle zone fasciculata, corticoids - Inner zone reticularis, androgen precursors, sex Main for stress response ```

Question 34

What is the stress response?

Answer 34

A state of real of perceived threat to homeostasis. Maintenance of homeostasis in the presence of stressors allows for activation of responses in endocrine, nervous and immune systems.

Question 35

Describe some of the changes during the stress repsonse.

Answer 35

Behavioural changes - increased awareness, improved cognition, euphoria, enhanced analgesia Physiological adaptations - increased heart rate and respiratory rate, increased immediated metabolism. Decrease in vegetative functions as not needed.

Question 36

Describe the pathway for the stress response.

Answer 36

Principle effectors are localised in the hypothalamus, anterior lobe of pituitary and adrenal gland. - Production of corticotrophic releasing hormone in hypothalamus. - Passes through HPP system into pituitary. - Corticotrophs in anterior pituitary allow production of adrenocorticotrophic hormone into blood. - ACTH receptors in adrenal cortex for response.

Question 37

How are chromaffin cells neurocrine secretion?

Answer 37

Sympathetic preganglionic signals pass down the spinal chord to the adrenal medulla, where chromaffin cells are the equivalent of post synaptic and release adrenaline.

Question 38

Describe the adrenal gland responses to stress.

Answer 38

Short term: - Nerve impulses to preganglionic fibres and adrenal medulla to cause release of catecholamines. Leads to increased heart rate, blood pressure, dilation of bronchioles, increased metabolic rate. Long term: - CRH to ACTH in pituitary, to adrenal cortex, corticoids. Leads to retention of sodium and water, increased blood pressure, increased blood sugar levels.

Question 39

Describe the structure of the pancreas.

Answer 39

Grouped into lobules which contain lobes, connected by connective tissue. Connect through numerous intercalated ducts to make pancreatic duct. Pancreatic duct joins with bile ducts to make common bile duct, which dumps all secretions into small intestine. Intercalated duct lined with cuboidal epithelium.

Question 40

Describe the endocrine gland component of the pancreas.

Answer 40

These are the islets of Langerhans. Alpha cells secrete glucagon. Beta cells secretes insulin. Delta cells produce somatostatin which inhibits these secretions. G cells gastrin, EC cells secretin (enterochromaffin)

Question 41

Describe the exocrine function of the pancreas.

Answer 41

These are the acini. Produce trypsinogen, chymotrypsinogen. Lipase, amylase, ribonuclease (and deoxy) elastase.