Endocrine System Flashcards
What are hormones?
- 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
How do hormones work?
How does the endocrine system work?
- 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
What are the two types of hormone?
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
Label the endocrine system
What is the endocrine system?
Function?
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
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Function - maintenance of homeostasis, growth, maturation etc
List the glands of the endocrine system?
The Glands of the Endocrine System
- •Pituitary gland
- •Pineal gland
- •Thyroid gland
- •Parathyroid gland
- •Islets of Langerhans (pancreas)
- •Adrenal glands
- •Gonads (covered in the lecture on the reproductive system)
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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
Outline the hypothalamus?
- 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.
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Where is the pituitary gland located with regards to other structures?
- 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
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What are the 2 lobes of the pituitary gland?
Anterior lobe
•Develops from upward growth of pharynx
Posterior lobe
•Downward projection from hypothalamic region
Outline the blood supply to the pituitary gland?
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
What 3 cells make up the anterior pituitary gland?
- Acidophils
- Basophils
- Chromophobes
What 2 cells make up the posterior pituitary gland?
- Non-myelinated nerve fibres
- Pituicytes
Explain the cellular structure of the anterior pituitary gland?
•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
Explain the cellular structure of the posterior pituitary gland?
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
What do acidophil cells secrete?
- Growth hormone
- Prolactin
What hormones do basophil cells secrete?
- Thyroid stimulating hormone
- Adrenocorticotrophic hormone
- Gonadotrophic hormones
What does the posterior pituitary gland store and secrete?
Key point to remember: it stores and releases antidiuretic hormone & oxytocin (secreted by the hypothalamus)
What fibres does the posterior pituitary gland contain?
What cells does the posterior pituitary gland contain?
- 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
What is the pineal gland made up of?
What does it secrete?
What controls the secretion?
Other functions?
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
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Describe the location of the pineal gland in relation to other parts of the brain?
- 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
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Where does the thyroid gland lie?
What is it’s structure?
Length, width?
Normal variant?
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)
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Describe the structure of the thyroid gland?
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
How many parathyroid glands are there usually?
Where?
Size?
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
What is being shown in this diagram?
Outline the structure of the parathyroid glands?
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
Where are the adrenal glands situated?
Shape?
Size?
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
How does the hypothalamus influence the adrenal gland portions?
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.
Explain the structure of the adrenal glands?
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
Outline the adrenal cortex of the adrenal glands?
Layers?
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
Outline the adrenal medulla of the adrenal glands?
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
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What are the 4 zones of the adrenal glands?
- Zona fasciculata
- Zona glomerulosa
- Zona reticularis
- The adrenal medulla
What does the zona fasciculta secrete?
Zona fasciculata
•Glucocorticoids- The principal glucocorticoid is cortisol, which increases blood glucose levels
What does the zona glomerulosa secrete?
Zona glomerulosa
•Mineralocorticoids - The principal mineralocorticoid is aldosterone, which acts to conserve sodium ions and water in the body
What does the zona reticularis secrete?
Zona reticularis – Male hormones, androgens and female hormones, estrogens
What does the adrenal medulla secrete?
The adrenal medulla – adrenaline(epinephrine) and noradrenaline (norepinephrine). These two hormones are secreted in response to stimulation by sympathetic nerve, particularly during stressful situations
What are the islets of langerhans?
Where most numerous?
What 3 types are there?
What do they secrete?
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)
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- Beta cells – secrete insulin
- Alpha cells – secrete glucagon
- Delta cells – secrete somatostatin
Explain the chain of reactions caused by the presence of food in the stomach?
•The lining of the stomach, the gastric mucosa, produces a hormone, called gastrin, in response to the presence of food in the stomach.
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•This hormone stimulates the production of hydrochloric acid and the enzyme pepsin, which are used in the digestion of food
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•The mucosa of the small intestine secretes the hormones secretin and cholecystokinin.
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- 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.
