The endocrine system Flashcards
What does the endocrine system consist of?
Endocrine cells and tissues
What type of cells are endocrine cells?
Epithelial glandular cells surrounded by an extensive network of capillaries
What is the difference between endocrine and exocrine cell?
Endocrine release hormones directly into the blood stream whereas exocrine release secretions into epithelial surfaces via ducts
What is the difference between endocrine tissue and endocrine glands?
Endocrine tissues may have other functions apart from hormones secretion however endocrine glands exclusively produce hormones
Is the endocrine system slower or faster acting that the CNS?
Slower
What are the two main divisions of hormones?
Lipid-soluble and water soluble
What kind of hormones are steroid hormones?
Lipid-soluble
What kind of hormones are thyroid hormones?
Lipid-soluble
What kind of hormones are amine hormones?
Water-soluble
What kind of hormones are peptide hormones?
Water-soluble
What kind of hormones are protein hormones?
Water-soluble
What can hormones be generally described as?
Chemical messengers
What mechanism occurs when hormones reach their target cell?
They bind to receptors affecting metabolic or chemical reactions inside the cell
Where are the receptors for water-soluble hormones found?
On the cell membrane
Where are the receptors for lipid-soluble hormones found?
Inside the cell
Do most hormones work under a positive or negative feedback system?
Negative
What cellular changes do hormones usually produce?
MS MS E
Membrane: changes permeability, potential or both by opening or closing ion channels.
Synthesis: of enzymes and other proteins within the cell.
Mitosis: Stimulation
Secretory activity: Induction
Enzymes: Activation or deactivation
What macro processes do hormones affect?
Growth
Metabolism
Homeostasis
Development
What is the hypophysis?
The pituitary gland
What is the difference in tissue type between the anterior and posterior pituitary glands?
The anterior is an upgrowth of epithelial tissue from the pharynx
The posterior is a down growth of nervous tissue from the brain
What is the adenohypophesis?
The anterior pituitary gland
What is the neurohypophesis?
The posterior pituitary gland
What structures allow the hypothalamus to communicate with the posterior pituitary gland?
A network of nerve fibres
What blood supply does the anterior pituitary gland have?
An indirect arterial supply that has passed via the capillaries of the hypothalamus
Why does the blood supply for the anterior pituitary gland come via the hypothalamus?
To allow hormones from the hypothalamus to reach the anterior pituitary gland directly
What are tropic hormones?
Hormones that have other endocrine glands as their target
Where are most tropic hormones produced?
The anterior pituitary gland
What are the anterior pituitary gland hormones?
Growth hormone
Prolactin
Luteinising hormone (LH)
Follicle stimulating hormone (FSH)
Thyroid stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
What is growth hormone?
A protein hormone that stimulates the growth of bone and muscle in growing children. It promotes protein synthesis and fat metabolism and acts as an insulin antagonist.
What is prolactin?
A protein hormone that is essential for lactation in the female.
What is luteinising hormone?
A glycoprotein that stimulates the production of testosterone in the testis, the ovulation and the secretion of oestrogen and progesterone by the ovary.
What is Follicle stimulating hormone (FSH)?
A glycoprotein that stimulates the formation of sperm in the testis and the maturation of the ovarian follicles and oestrogen in the ovary.
What is Thyroid stimulating hormone (TSH)?
A glycoprotein that stimulates the synthesis and secretion of thyroid hormones T4 and T3.
What is Adrenocorticotropic hormone (ACTH)?
An anterior pituitary gland peptide hormone that stimulates the synthesis and secretion of the glucocorticoid and adrenal androgens (sex hormones) by the adrenal cortex
What is the function of the posterior pituitary gland?
It stores hormones produced by the hypothalamus
What blood supply does the posterior pituitary gland have?
Direct arterial blood supply from the internal carotid (via the inferior hypophyseal artery)
What are the posterior pituitary hormones?
Anti diuretic hormone (ADH)
Oxytocin
What is Vasopressin or Anti-Diuretic Hormone (ADH) and when is it released?
A short peptide that is secreted by the posterior pituitary in response to elevated plasma osmolarity (high salt or low water content) or decreased blood volume. It increases the permeability of the distal convoluted tubules and collecting ducts to increase water retention and causes arteriole construction increasing peripheral vascular resistance.
What is oxytocin?
It stimulates uterine contraction during labour and the contraction of breast ducts during lactation
What gives the thyroid gland its colouration?
The thyroid gland is deep red due to large numbers of blood vessels
What is the macrostructure of the thyroid gland?
Two lobes connected by the isthmus covered by a fibrous sheet
What are the microstructures of the thyroid gland?
The thyroid gland is formed of small spherical sacs called thyroid follicles. The wall of the follicles consist primarily of cuboidal epithelial cells that are surrounded by a basement membrane. Parafolicular cells (C cells) lie inbetween follicles
What hormone affects the follicle cells in the thyroid?
Thyroid stimulating hormone (TSH)
Where is thyroid stimulating hormone producted and what stimulates it?
It is produced in the hypothalamus under the stimulating effect of the hypothalamic hormone Thyrotropin-Releasing Hormone (TRH)
What are the two thyroid hormones?
Thyroxine (T4)
Tri-iodothyronine (T3)
How much of T4 and T3 respectively does the thyroid gland produce?
Mainly T4 and small amounts of T3
Where is most T3 produced?
Outside the thyroid gland in other tissues such as liver, kidney and muscle
Is T3 or T4 more active?
T3 is much more active
What are the main functions of T3 and T4?
Regulate growth, development and reproduction
Stimulate metabolic activities (proteins, carbohydrates and fats) Energy production and utilisation
Increase sensitivity of the cardiovascular and nervous system to adrenaline and noradrenaline
What are parafollicular cells?
C-cells. Cells in the thyroid gland that lie inbetween the follicles.
What is calcitonin?
A thyroid hormone that lowers blood calcium levels by promoting the storage of calcium in bone tissue and inhibiting it’s re absorption in the kidneys
What are the parathyroid glands?
Two pairs (four in total) of tiny rounded masses of tissue embedded in the posterior surfaces of the thyroid gland.
One superior and one inferior parathyroid gland are attached to the right and left thyroid lobes.
What cells do the parathyroid glands contain?
Two types of epithelial cells, the more numerous chief cells which produce Parathyroid Hormones (PTH), and another form of cells which have an unknown function
What is the main function of PTH?
To increase blood calcium levels (opposite to the action of calcitonin of the thyroid gland). This is achieved by increasing the calcium absorption from the small intestine and calcium reabsorption from the kidney tubules. It also releases calcium from bones into the blood by stimulating osteoclasts (bone-destroying cells).
What is the structure of the adrenal glands?
Adrenal medulla and cortex surrounded by a capsule. Highly vascular
What is the internal structure of the adrenal medulla?
Three different zones the outer, middle and inner
What does the outer zone of the adrenal medulla produce?
Mineral corticoids
What does the middle zone of the adrenal medulla produce?
Glucocorticoids
What does the inner zone of the adrenal medulla produce?
Androgens
What are androgens?
Sex hormones
What is kind of hormone is aldosterone?
Mineralcorticoid steroid hormone
What is the action of aldosterone?
It encourages sodium reabsorption, water retention and potassium excretion
What levels stimulates aldosterone secretion?
High blood potassium
Where is aldosterone synthesised and secreted?
The outer layer of the adrenal cortex, the zona glomerulosa
What is the RAAS?
The renin-angiotensin-aldosterone system (RAAS) is a well known regulator of blood pressure (BP) and determinant of target-organ damage. It controls fluid and electrolyte balance through coordinated effects on the heart, blood vessels, and Kidneys.
What class of hormones are cortisol, corticosterone and cortisone?
Glucocorticoids
What controls the secretion of glucocorticoids (e.g. cortisol) from the adrenal gland?
Adrenocorticotropic hormone (ACTH)
What are the main effects of glucocorticoids (cortisone and hydrocortisone)?
Glucose formation
Lipolysis
Stimulating protein catabolism
Promoting sodium and water retention
Suppression of immune responses
Delayed wound healing
Where are weak sex hormones secreted?
By the adrenal cortex in both males and females, in small amounts
Where does the adrenal cortex originate from?
It is a modified sympathetic ganglion of the ANS, with the same embryonic origin
What will an extensive sympathetic stimulation of the adrenal medulla cause?
The release of adrenaline and noradrenaline
In what proportion does the adrenal medulla release adrenaline and noradrenaline?
80% adrenaline
20% noradrenaline
What is the structure of pancreatic tissue?
Clusters of pancreatic acini with pancreatic islets scattered within. Abundant capillaries serve both types of tissue.
What is the distribution of acini and islets in the pancreas?
99% acini, 1% islets
What is the endocrine tissue of the pancreas?
Islets
What is the exocrine tissue of the pancreas?
Acini
What is the function of pancreatic acini?
They produce digestive enzymes that are secreted into the GI tract through the pancreatic duct
What types of cells are present in pancreatic islets?
Alpha (A)
Beta (B)
Delta (D)
F
What is the function of pancreatic A cells?
Glucagon secretion
What is the function of pancreatic B cells?
Insulin secretion
What is the function of pancreatic D cells?
Somatostatin secretion
What is the function of pancreatic F cells?
Pancreatic polypeptide secretion
Where is somatostatin produced?
GI tract
Pancreas
Hypothalamus
CNS
What is the function of somatostatin?
Inhibiting the secretion of both insulin and glucagon from the pancreas.
Inhibiting the secretion of of growth hormone (GH) from the anterior pituitary
What does insulin enhance?
Oxidation and energy generation
What does insulin increase?
Glycogenesis (formation of glycogen)
What does insulin accelerate?
Protein synthesis and lipogenesis
What does insulin decelerate?
Glycogenolysis and gluconeogenesis
How does insulin drop blood glucose?
-Enhancing oxidation and energy generation
-Increasing glycogenesis
-Accelerating protein synthesis
-Accelerating lipogenesis
-Decelerating glycogenolysis
-Decelerating gluconeogenesis
What are examples of insulin antagonists?
Glucagon, adrenaline, cortisol and growth hormone all have insulin-antagonist effects
How do insulin antagonists counter its effects?
Acting on the liver cells to speed glycogenolysis
Acting on the muscles to speed gluconeogenesis
What are the gonads?
Male and female reproductive organs.
Ovaries and testes.
What is the function of the gonads?
Gamete and hormone production
What steroids do the ovaries produce?
Several steroid hormones including oestrogens and progesterone
What is the purpose of female sex hormones?
Regulation of menstrual cycle, maintaining pregnancy, preparing mammary glands for lactation, development and maintenance of secondary sex characteristics
What is the main hormone produced in the testes?
Testosterone
What is the function of testosterone?
Stimulate descent of testes, regulation of sperm production, development and maintenance of secondary sex characteristics
Where is the pineal gland located?
Attached to the third ventricle of the brain at the midline, part of the epithalamus
How does the pineal gland develop?
Develops normally until after puberty when it tends to atrophy and my be calcified in later life
What is the main hormone of the pineal gland?
Melatonin
What are the functions of melatonin?
Not exactly know but believe to be involved in:
Circadian and diurnal rhythm of many tissues
Inhibition of growth and development of sex organs before puberty
Does the endocrine system make precise or approximate adjustments?
Precise
Which type of hormones have longer half lives and why?
Lipid-soluble as they must be transported by carrier proteins and their receptors lie inside cells.
They must be released from their transport proteins and then diffuse through the cell membrane
Why are steroid proteins lipid-soluble and not water-soluble?
They are built around a cholesterol core and uncharged
Why are steroid proteins lipid-soluble and not water-soluble?
They are built around a cholesterol core and uncharged
Why are thyroid hormones lipid-soluble and not water-soluble?
They contain benzene rings which increase lipid-solubility and iodine atoms which decrease water-solubility
Why are amine, peptide and protein hormones water-soluble and not lipid-soluble?
They are charged molecules which attract “spheres of hydration” and allow them to flow through water as a larger and therefore less lipid-soluble structure
How does the hypothalamus transport hormones to the posterior pituitary?
Via a bridge of nerve axons called the hypothalamic–hypophyseal tract
What stimulates the release of thyrotropin releasing hormone (TRH)?
Insufficient levels of thyroid hormone being available for the brain
What do parafollicular cells do?
Produce Calcitonin
What are pancreatic islets also known as?
Islets of Langerhans
What are glucocorticoids named after?
Their roles in maintaining glucose homeostasis
What are mineralcorticoids named after?
Their roles in maintaining electrolyte balance
How is calcium homeostasis maintained?
