Endocrine System

Question 1

What are hormones?

Answer 1

• Hormones act as mediator molecules, they are released in one part of the body but, often regulate the activity of cells in another part of the body
• Hormones are (generally) carried by the blood that circulates throughout the body
• The nervous and endocrine systems act in unison to coordinate and regulate ALL the body systems

Question 2

How do hormones work?

How does the endocrine system work?

Answer 2

• Hormones exert their effect by binding to receptors in their “target” cells
• The endocrine system functions on a slower time scale than the nervous system does. The organs that make up the endocrine system are called the endocrine glands, and these communicate with the body by releasing chemical messengers (hormones) into the bloodstream

Question 3

What are the two types of hormone?

Answer 3

Central control (circulating hormones)

• These coordinate biological processes over the entire body

Local control (local hormones)

• Autocrine secretions acting on the cells they originate from
• Paracrine secretions that act on the cells in the surrounding tissue

Question 4

Label the endocrine system

Answer 4

Question 5

What is the endocrine system?

Function?

Answer 5

The Endocrine System

• Consists of a number of glands
• The glands are widely distributed around the body
• ‘Ductless’ glands because the secretions pass straight into the blood stream
• Secrete hormones

•

Function - maintenance of homeostasis, growth, maturation etc

Question 6

List the glands of the endocrine system?

Answer 6

The Glands of the Endocrine System

1. •Pituitary gland
2. •Pineal gland
3. •Thyroid gland
4. •Parathyroid gland
5. •Islets of Langerhans (pancreas)
6. •Adrenal glands
7. •Gonads (covered in the lecture on the reproductive system)

•

Other Endocrine Glands

• The hypothalamus may also be considered part of the endocrine system
• Certain cells in the gastrointestinal system also secrete hormones
• These structures will be considered in the lecture on the central nervous system, and in the gastrointestinal lecture

Question 7

Outline the hypothalamus?

Answer 7

• The hypothalamus is the master of the hormone system; it has the task of ensuring the internal stability of the human body (homeostasis).
• At every moment, the hypothalamus assesses messages coming to it from the brain and the throughout the body.
• It has a number of essential functions, acting to maintain a stable body temperature, by controlling blood pressure, ensuring a fluid balance, and even directing sleep patterns.

Question 8

Label this image

Answer 8

Question 9

Where is the pituitary gland located with regards to other structures?

Answer 9

• Lies in the sella turcica (pituitary fossa) of the sphenoid bone
• Attached inferiorly to the hypothalamus by a thin stalk – the pituitary stalk
• The optic chiasma (communicating tract between the two optic nerves) lies immediately anterior to the pituitary gland
• The sphenoid sinus lies anterior and inferior to the pituitary fossa
• The cavernous sinuses (venous channels containing the internal carotid artery, and certain cranial nerves) run either side of the pituitary fossa

Question 10

Label image

Answer 10

Question 11

What are the 2 lobes of the pituitary gland?

Answer 11

Anterior lobe

•Develops from upward growth of pharynx

Posterior lobe

•Downward projection from hypothalamic region

Question 12

Outline the blood supply to the pituitary gland?

Answer 12

Blood Supply

• Branches of the internal carotid and posterior cerebral arteries supply the posterior pituitary gland, the pituitary stalk and parts of the hypothalamus
• Veins that drain from the hypothalamus form the hypophysial portal system
• The hypophysial portal system supplies blood to the anterior pituitary gland
• Hence the hypothalamus can regulate the function of the anterior pituitary gland

Question 13

What 3 cells make up the anterior pituitary gland?

Answer 13

• Acidophils
• Basophils
• Chromophobes

Question 14

What 2 cells make up the posterior pituitary gland?

Answer 14

• Non-myelinated nerve fibres
• Pituicytes

Question 15

Explain the cellular structure of the anterior pituitary gland?

Answer 15

•The Anterior Pituitary Gland

Contains 3 main types of hormone secreting cells:

• Acidophil – growth hormone, prolactin
• Basophil – TSH, ACTH, gonadotrophic hormones
• Chromophobe – thought to be capable of secreting ACTH

Question 16

Explain the cellular structure of the posterior pituitary gland?

Answer 16

The Posterior Pituitary Gland

• Contains thin, non-myelinated nerve fibres
• These nerve fibres are the termination of modified nerve tracts whose cell bodies lie within the hypothalamus
• Contains specialised glial cells – pituicytes
• ADH and oxytocin are produced by the hypothalamus and are transported along the nerve fibres to the posterior pituitary gland by a process called neurosecretion
• They are stored in the posterior pituitary gland until they are required to be released into the circulation

Question 17

What do acidophil cells secrete?

Answer 17

• Growth hormone
• Prolactin

Question 18

What hormones do basophil cells secrete?

Answer 18

• Thyroid stimulating hormone
• Adrenocorticotrophic hormone
• Gonadotrophic hormones

Question 19

What does the posterior pituitary gland store and secrete?

Answer 19

Key point to remember: it stores and releases antidiuretic hormone & oxytocin (secreted by the hypothalamus)

Question 20

What fibres does the posterior pituitary gland contain?

What cells does the posterior pituitary gland contain?

Answer 20

• Contains thin, non-myelinated nerve fibres
• These nerve fibres are the termination of modified nerve tracts whose cell bodies lie within the hypothalamus
• Contains specialised glial cells – pituicytes
• ADH and oxytocin are produced by the hypothalamus and are transported along the nerve fibres to the posterior pituitary gland by a process called neuro-secretion

Question 21

What is the pineal gland made up of?

What does it secrete?

What controls the secretion?

Other functions?

Answer 21

Specialised cells: pinealocytes plus neuro-glial cells

Secretes melatonin

Secretions controlled by ambient light levels

Involved in sexual function & development?

Modulation of wake/sleep patterns

Question 22

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Answer 22

Question 23

Describe the location of the pineal gland in relation to other parts of the brain?

Answer 23

• Located anteriorly to third ventricle in pineal recess
• It is posterior and inferior to the superior cerebella cistern
• It is superior to cerebral veins and vein of Galen
• Sits superior to the superior colliculi of the midbrain and near optic pathways

Question 24

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Answer 24

Question 25

Where does the thyroid gland lie? What is it's structure? Length, width? Normal variant?

Answer 25

The Thyroid Gland * Lies in the lower anterior region of the neck * Consists of two lobes * The lobes lie either side of the trachea and are joined by a narrow isthmus * Each lobe is about 5 cm long and 2 – 3 cm across at its widest point * A normal variant is the presence of a pyramidal lobe (small extra lobe that arises from the superior border of the isthmus)

Question 26

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Answer 26

Question 27

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Answer 27

Question 28

Describe the structure of the thyroid gland?

Answer 28

The Structure of the Thyroid Gland * Covered by a thin connective tissue capsule * Consists of a large number of spherical follicles * The spherical follicles are lined with cuboidal epithelium containing colloid * The colloid consists of a glycoprotein, thyroglobulin, which is the stored form of the thyroid hormones * Parafollicular cells are also present, but in smaller numbers than the follicular cells * Parafollicular cells secrete calcitonin

Question 29

How many parathyroid glands are there usually? Where? Size?

Answer 29

The Parathyroid Glands * Usually four parathyroid glands * Two lie on the posterior surface of each lobe of the thyroid gland * Small – about 6 mm by 3 mm by 2 mm * Do vary in number, may have 3 – 6 + * Anatomical location may vary i.e. can be ectopic

Question 30

What is being shown in this diagram?

Answer 30

Question 31

Outline the structure of the parathyroid glands?

Answer 31

Structure of the Parathyroid Glands * Thin connective tissue capsule * The cells, chief cells, are arranged in columns * The chief cells are classified as light, dark or clear cells (depending on their staining characteristics) * The chief cells secrete parathyroid hormone * Oxyphil cells are also present but do not secrete hormones

Question 32

Where are the adrenal glands situated? Shape? Size?

Answer 32

The Adrenal Glands * Retroperitoneal * Situated on the upper pole of each kidney * Surrounded by adipose tissue * Lie within the renal fascia * Right adrenal gland - roughly pyramidal * Left adrenal gland – roughly crescentric * About 5 cm long and 3 cm thick

Question 33

How does the hypothalamus influence the adrenal gland portions?

Answer 33

The hypothalamus of the brain influences both portions of the adrenal gland but by different mechanisms. * The adrenal cortex is regulated by negative feedback involving the hypothalamus and adrenocorticotropic hormone * The medulla is regulated by nerve impulses from the hypothalamus.

Question 34

Explain the structure of the adrenal glands?

Answer 34

The Structure of the Adrenal Glands * Outer cortex – three layers, and makes up about 90% of the glands’ total weight * Inner medulla * Accessory adrenal glands are sometimes found in the fat surrounding the adrenal glands or renal cortex

Question 35

Outline the adrenal cortex of the adrenal glands? Layers?

Answer 35

The Adrenal Cortex * The outer layer, zona glomerulosa, composed of small polyhedral cells, arranged in clumps * The middle layer, zona fasciculata, large polyhedral cells, arranged in columns * The inner layer, zona reticularis, network of rounded cells

Question 36

Outline the adrenal medulla of the adrenal glands?

Answer 36

The Adrenal Medulla * Composed of groups and columns of cells * These cells are called chromaffin cells * Derived from cells which form the sympathetic nervous system * Nerve cells are scattered amongst the chromaffin cells

Question 37

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Answer 37

Question 38

What are the 4 zones of the adrenal glands?

Answer 38

1. Zona fasciculata 2. Zona glomerulosa 3. Zona reticularis 4. The adrenal medulla

Question 39

What does the zona fasciculta secrete?

Answer 39

Zona fasciculata •Glucocorticoids- The principal glucocorticoid is cortisol, which increases blood glucose levels

Question 40

What does the zona glomerulosa secrete?

Answer 40

Zona glomerulosa •Mineralocorticoids - The principal mineralocorticoid is aldosterone, which acts to conserve sodium ions and water in the body

Question 41

What does the zona reticularis secrete?

Answer 41

Zona reticularis – Male hormones, androgens and female hormones, estrogens

Question 42

What does the adrenal medulla secrete?

Answer 42

The adrenal medulla – adrenaline(epinephrine) and noradrenaline (norepinephrine). These two hormones are secreted in response to stimulation by sympathetic nerve, particularly during stressful situations

Question 43

What are the islets of langerhans? Where most numerous? What 3 types are there? What do they secrete?

Answer 43

The Islets of Langerhans * Collections of endocrine cells * Interspersed amongst the exocrine cells of the pancreas * Are most numerous in the tail of the pancreas * Have a rich blood supply and sympathetic autonomic, and parasympathetic nerve supply * Different types of cells * Secrete insulin, glugagon, somatostatin (plus some other hormones whose role is not yet clear) • • * Beta cells – secrete insulin * Alpha cells – secrete glucagon * Delta cells – secrete somatostatin

Question 44

Explain the chain of reactions caused by the presence of food in the stomach?

Answer 44

•The lining of the stomach, the gastric mucosa, produces a hormone, called gastrin, in response to the presence of food in the stomach. • •This hormone stimulates the production of hydrochloric acid and the enzyme pepsin, which are used in the digestion of food • •The mucosa of the small intestine secretes the hormones secretin and cholecystokinin. • * Secreting these hormones stimulates the pancreas to produce a bicarbonate-rich fluid that neutralizes the stomach acid. * Cholecystokinin stimulates contraction of the gallbladder, which releases bile, in addition it stimulates the pancreas to secrete digestive enzyme.