The endocrine system
● The hypothalamus, pituitary gland, thyroid, parathyroid, pancreas,
thymus, gonads, pineal and adrenal glands, that are endocrine glands
found in the human body.
-The endocrine system regulates the activity of cells by sending out hormones, they are
chemical messengers.
- The endocrine system maintains a constant environment inside of the body called
homeostasis.
-When the body experiences a change it is a stimulus.
Endocrine glands (Ductless glands)
-Endocrine glands release hormones to the extra-cellular fluid that surround the cells of the
gland.
-The secretions pass through the capillaries
-They get to the bloodstream to be transported to the target organs.
Exocrine glands
-Exocrine glands secrete substances out to the epithelial surface (external surface) via a
duct.
-Examples are sweat glands, oil glands, salivary glands, mucous glands etc.
● Explain how hormones secreted from the hypothalamus, pituitary,
thyroid, parathyroid, thymus, gonads, pineal, pancreas and adrenal
glands are involved in homeostasis by affecting specific target organs.
Hypothalamus
-It is located in the base of the brain
-regulates body temperature, water balance and heart rate, sleep patterns, eating patterns.
-A lot of functions of the hypothalamus happen in the pituitary gland A.K.A ‘Master gland’
-The hypothalamus produces releasing and inhibiting factors for the anterior lobe and it
produces hormones ADH and oxytocin for the posterior lobe.
-The posterior lobe is connected by nerve fibers that run through infundibulum.
-The anterior lobe is connected by complex blood vessels in the infundibulum.
The production of hormones in the hypothalamus
,There are two sets of nerve cells in the hypothalamus that produce hormones. One set
sends the hormones they produce down through the pituitary stalk to the posterior lobe.
The other set produces releasing and inhibiting factors that get sent down the complex
blood vessels in the infundibulum to the anterior lobe where they are then stored and
released when needed.
Anterior lobe
The anterior lobe secretes hormones that control many of the body’s activities.
Hormones start to release from the anterior lobe once ‘releasing factors’ have been
secreted from the hypothalamus. The hypothalamus also releases ‘inhibiting factors’ to slow
secretion down.
Hormones releases by the anterior lobe include:
-Gonadotropins (FSH, LH); Hormones that affect the sexual organs such as the testes and
ovaries.
-Follicle-stimulating hormone (FSH) in the ovary to stimulate the growth of eggs
-Growth hormone (GH) which stimulates body growth and maintains size of organs.
-Prolactin (PRL) which works with other hormones to help secret milk in females.
-Thyrotropin or (TSH) which stimulates production or release of thyroid hormones
-Adrenocorticotrophic (ACTH) hormone controls the production and release of hormones
from the adrenal cortex
Posterior lobe
The Oxytocin and ADH hormones are produced by a special set nerve cells in the
hypothalamus that travel through long nerve extensions in the infundibulum to the
posterior lobe where they are then stored and then released into the bloodstream.
Hormones released by the posterior lobe are:
-Oxytocin which stimulates the contraction of muscles in the uterus and also the cells of
mammary glands to release milk.
-Antidiuretic (Vasopressin) hormone allows water reabsorption into the collecting duct so
more fluid is available for the body. It also constricts small arteries. Hence, that’s why it’s
also called vasopressin. Anti-diuretic literally means ‘anti-peeing’. So urination is decreased.
It’s usually released in hot environments or when dehydrated. It also decreases the
permeability of the distal convoluted tubule so less water becomes enters the tubule to
become filtrate.
Pineal gland
It is located deep in the brain, on top of the mouth. Not much is known by scientists about
it. It is known to release melatonin in dark environments such as when you are getting ready
to go to bed.
Thyroid
-It’s located in the neck
,-Two lobes that lay either side of neck connected by tissue
-It uses iodine and amino acid to make two hormones, T3 (Triiodithyronine) and T4
(thyroxine)
- T3 and T4 are released in response to Thyroid-Stimulating hormone from anterior lobe.
-Controls reactions in which complex molecules are broken down to release energy and
reactions where simple molecules are synthesized into complex ones.
-Releases energy in form of heat so it maintains body temperature.
-T3 and T4 regulate cellular respiration/the heart rate/digestion speed.
Parathyroid
-There are usually 4 parathyroid glands.
-They are found at the back surface of the thyroid gland.
-They control phosphate (P) and calcium (Ca) levels in the blood.
-Effects bones, intestines and kidneys
Thymus
-It’s located above chest below the thyroid gland.
-Releases thymosins which mature T-lymphocytes; disease fighting cells.
-Shrinks after puberty and as you age.
Gonads
-They are testes and ovaries
-Androgens are male sex hormones produced by testes, it helps develop secondary male
characteristics.
-Oestrogen is a female sex hormone produced by the ovaries, it regulates the menstrual
cycle and sexual characteristics.
Adrenal glands
-There are 2 adrenal glands and 1 is located above each kidney.
- Each adrenal gland has an adrenal medulla and adrenal cortex
Adrenal medulla
-Inner portion of adrenal gland
-Produces adrenaline or epinephrine which increases heart rate in a threatening situation in
which the fight or flight response occurs.
-Produces noradrenalin which is similar to adrenaline but increases rate and force of heart
rate.
Adrenal cortex
-Outer portion of adrenal gland
, -Produces cortisol which with the help of other hormones helps body withstand stress,
repairs damaged tissues and promotes normal metabolism
-Produces aldosterone which acts on the distal convoluted tubule to secrete potassium in
the filtrate and to reabsorb chloride back to the bloodstream along with water.
Pancreas
-Lies below the stomach beside the duodenum (first part of intestine)
- It is both and endocrine and exocrine gland
-Special cells called islets-of-langerhans are the endocrine part of the pancreas
-The beta cells release insulin and the alpha cells release glucagon.
-Both help regulate levels of blood glucose
Insulin
-reduces glucose in the blood (blood sugar level)
-Promotes uptake of glucose from blood by cells of body to helps body get the energy from
the food we need vya cellular respiration.
-In liver, converts glucose into glycogen and fat.
-In fat tissue, converts glucose into fat.
-In skeletal muscles, converts glucose into glycogen.
Glucagon
-opposite of insulin
-Increases blood sugar level
-In liver, breaks down glycogen into glucose
-In fat tissue, breaks down fat into glucose.
● Discuss how hormones can be lipid-soluble and be able to cross cell
membranes to bind with and activate intracellular receptors or, water-
soluble and able to bond with or activate receptors on cell membranes,
and require secondary messengers to affect cell functioning.
-Cells can communicate with other cells in same tissue by secreting chemicals that diffuse
through adjacent cells; these substances are called Paracrines A.K.A Local Hormones
-Paracrines are secreted by all cells and move through extracellular fluid.
-Hormones are released by specialized cells and are very specific. They are transported by the
bloodstream to the target cell and the hormone receptors on the cell can become saturated.
-Protein and amines (end with ‘in’, ‘ine’) attach to receptor proteins found on the membranes
of the cell
-When a hormone and a receptor combine, a secondary messenger called Cyclic AMP (cAMP)
diffuses through the cell to activate a certain enzyme to cause change to the cell.
● The hypothalamus, pituitary gland, thyroid, parathyroid, pancreas,
thymus, gonads, pineal and adrenal glands, that are endocrine glands
found in the human body.
-The endocrine system regulates the activity of cells by sending out hormones, they are
chemical messengers.
- The endocrine system maintains a constant environment inside of the body called
homeostasis.
-When the body experiences a change it is a stimulus.
Endocrine glands (Ductless glands)
-Endocrine glands release hormones to the extra-cellular fluid that surround the cells of the
gland.
-The secretions pass through the capillaries
-They get to the bloodstream to be transported to the target organs.
Exocrine glands
-Exocrine glands secrete substances out to the epithelial surface (external surface) via a
duct.
-Examples are sweat glands, oil glands, salivary glands, mucous glands etc.
● Explain how hormones secreted from the hypothalamus, pituitary,
thyroid, parathyroid, thymus, gonads, pineal, pancreas and adrenal
glands are involved in homeostasis by affecting specific target organs.
Hypothalamus
-It is located in the base of the brain
-regulates body temperature, water balance and heart rate, sleep patterns, eating patterns.
-A lot of functions of the hypothalamus happen in the pituitary gland A.K.A ‘Master gland’
-The hypothalamus produces releasing and inhibiting factors for the anterior lobe and it
produces hormones ADH and oxytocin for the posterior lobe.
-The posterior lobe is connected by nerve fibers that run through infundibulum.
-The anterior lobe is connected by complex blood vessels in the infundibulum.
The production of hormones in the hypothalamus
,There are two sets of nerve cells in the hypothalamus that produce hormones. One set
sends the hormones they produce down through the pituitary stalk to the posterior lobe.
The other set produces releasing and inhibiting factors that get sent down the complex
blood vessels in the infundibulum to the anterior lobe where they are then stored and
released when needed.
Anterior lobe
The anterior lobe secretes hormones that control many of the body’s activities.
Hormones start to release from the anterior lobe once ‘releasing factors’ have been
secreted from the hypothalamus. The hypothalamus also releases ‘inhibiting factors’ to slow
secretion down.
Hormones releases by the anterior lobe include:
-Gonadotropins (FSH, LH); Hormones that affect the sexual organs such as the testes and
ovaries.
-Follicle-stimulating hormone (FSH) in the ovary to stimulate the growth of eggs
-Growth hormone (GH) which stimulates body growth and maintains size of organs.
-Prolactin (PRL) which works with other hormones to help secret milk in females.
-Thyrotropin or (TSH) which stimulates production or release of thyroid hormones
-Adrenocorticotrophic (ACTH) hormone controls the production and release of hormones
from the adrenal cortex
Posterior lobe
The Oxytocin and ADH hormones are produced by a special set nerve cells in the
hypothalamus that travel through long nerve extensions in the infundibulum to the
posterior lobe where they are then stored and then released into the bloodstream.
Hormones released by the posterior lobe are:
-Oxytocin which stimulates the contraction of muscles in the uterus and also the cells of
mammary glands to release milk.
-Antidiuretic (Vasopressin) hormone allows water reabsorption into the collecting duct so
more fluid is available for the body. It also constricts small arteries. Hence, that’s why it’s
also called vasopressin. Anti-diuretic literally means ‘anti-peeing’. So urination is decreased.
It’s usually released in hot environments or when dehydrated. It also decreases the
permeability of the distal convoluted tubule so less water becomes enters the tubule to
become filtrate.
Pineal gland
It is located deep in the brain, on top of the mouth. Not much is known by scientists about
it. It is known to release melatonin in dark environments such as when you are getting ready
to go to bed.
Thyroid
-It’s located in the neck
,-Two lobes that lay either side of neck connected by tissue
-It uses iodine and amino acid to make two hormones, T3 (Triiodithyronine) and T4
(thyroxine)
- T3 and T4 are released in response to Thyroid-Stimulating hormone from anterior lobe.
-Controls reactions in which complex molecules are broken down to release energy and
reactions where simple molecules are synthesized into complex ones.
-Releases energy in form of heat so it maintains body temperature.
-T3 and T4 regulate cellular respiration/the heart rate/digestion speed.
Parathyroid
-There are usually 4 parathyroid glands.
-They are found at the back surface of the thyroid gland.
-They control phosphate (P) and calcium (Ca) levels in the blood.
-Effects bones, intestines and kidneys
Thymus
-It’s located above chest below the thyroid gland.
-Releases thymosins which mature T-lymphocytes; disease fighting cells.
-Shrinks after puberty and as you age.
Gonads
-They are testes and ovaries
-Androgens are male sex hormones produced by testes, it helps develop secondary male
characteristics.
-Oestrogen is a female sex hormone produced by the ovaries, it regulates the menstrual
cycle and sexual characteristics.
Adrenal glands
-There are 2 adrenal glands and 1 is located above each kidney.
- Each adrenal gland has an adrenal medulla and adrenal cortex
Adrenal medulla
-Inner portion of adrenal gland
-Produces adrenaline or epinephrine which increases heart rate in a threatening situation in
which the fight or flight response occurs.
-Produces noradrenalin which is similar to adrenaline but increases rate and force of heart
rate.
Adrenal cortex
-Outer portion of adrenal gland
, -Produces cortisol which with the help of other hormones helps body withstand stress,
repairs damaged tissues and promotes normal metabolism
-Produces aldosterone which acts on the distal convoluted tubule to secrete potassium in
the filtrate and to reabsorb chloride back to the bloodstream along with water.
Pancreas
-Lies below the stomach beside the duodenum (first part of intestine)
- It is both and endocrine and exocrine gland
-Special cells called islets-of-langerhans are the endocrine part of the pancreas
-The beta cells release insulin and the alpha cells release glucagon.
-Both help regulate levels of blood glucose
Insulin
-reduces glucose in the blood (blood sugar level)
-Promotes uptake of glucose from blood by cells of body to helps body get the energy from
the food we need vya cellular respiration.
-In liver, converts glucose into glycogen and fat.
-In fat tissue, converts glucose into fat.
-In skeletal muscles, converts glucose into glycogen.
Glucagon
-opposite of insulin
-Increases blood sugar level
-In liver, breaks down glycogen into glucose
-In fat tissue, breaks down fat into glucose.
● Discuss how hormones can be lipid-soluble and be able to cross cell
membranes to bind with and activate intracellular receptors or, water-
soluble and able to bond with or activate receptors on cell membranes,
and require secondary messengers to affect cell functioning.
-Cells can communicate with other cells in same tissue by secreting chemicals that diffuse
through adjacent cells; these substances are called Paracrines A.K.A Local Hormones
-Paracrines are secreted by all cells and move through extracellular fluid.
-Hormones are released by specialized cells and are very specific. They are transported by the
bloodstream to the target cell and the hormone receptors on the cell can become saturated.
-Protein and amines (end with ‘in’, ‘ine’) attach to receptor proteins found on the membranes
of the cell
-When a hormone and a receptor combine, a secondary messenger called Cyclic AMP (cAMP)
diffuses through the cell to activate a certain enzyme to cause change to the cell.
