7: The Endocrine System Flashcards
What is homeostasis?
Homeostasis is the control of body function. It requires the coordinated activity of the nervous and endocrine systems
Describe the actions of the endocrine system:
The actions of the endocrine system are much slower and longer than the nervous system
What chemical messengers does the endocrine system use?
The endocrine system uses hormones as chemical messengers secreted by the endocrine gland
Describe the actions of hormones in the endocrine system:
The endocrine system uses hormones secreted by the endocrine gland. This makes the action less targeted because the hormones are released into the bloodstream, exposing all cells
Describe the cell response to a hormone:
A cell will only respond to a particular hormone if it has a receptor for that hormone. The effect is long term because the hormone is effective for as long as it’s in the bloodstream
Describe the solubility of hormones:
Hormones move around the body in the blood, so need to be soluble in blood, which is a very watery substance. This means hormones need to be water soluble to be able to be soluble in blood
Many hormones are water soluble, making travelling easy. Other hormones are insoluble, so need special carry proteins to transport them
What is half life?
The time a hormone is active in the blood is called its half-life
Describe half life for hormones:
Half life is very variable in hormones. It depends on the activity of enzymes in the blood or liver that break down the hormone
What are receptor proteins?
Cells produce receptor proteins that bind to typically one particular hormone, activating specific cellular metabolic pathways and creating a change in cell behaviour
Water soluble hormones find their receptor in the cell membrane as they are able to pass through the lipid cell membrane and target their receptors intracellularly
What are the roles of hormones?
The roles of hormones are to:
- Regulate metabolism
- Control the rate of chemical reactions
- Help things move across cell membranes
- Regulate water and ion balances
- Vital role in reproduction and growth
What is the role of thyroid hormones?
Thyroid hormones regulate metabolism
What is the role of growth hormones?
Growth hormones control the rate of chemical reactions
What is the role of insulin?
Insulin helps things to move across cell membranes
What is the role of anti diuretic hormone?
ADH regulates water and ion balances
What is the role of oestrogen?
Oestrogen plays a vital role in reproduction and growth
Describe the relationship between the hypothalamus and pituitary gland:
There is a very close relationship between the hypothalamus in the brain and the pituitary gland which secretes hormones
The hypothalamus controls the pituitary
Describe the role of the pituitary gland:
The pituitary gland secretes hormones. It is often called the master gland because it controls many other glands
Describe the structure of the posterior pituitary:
The posterior pituitary develops from a stalk off of the floor of the brain (hypothalamus)
Describe the role of the posterior pituitary
Nerved from the hypophysis extend down into the posterior pituitary and produces neuron or ones that build up in the nerve terminals. When the hypothalamus is activated, these hormones are released into the blood supply and into the general body circulation
Describe the position of the anterior pituitary:
The posterior pituitary is connected to the anterior pituitary by a pocket of epithelial tissues that has disengaged from the oral cavity
Describe the role of the anterior pituitary:
Other nerves in the hypothalamus release neurohormones into their own capillary bed. Capillary vessels carry the neurohormone to the anterior pituitary. These neurohormones act upon he anterior cells either stimulating or inhibiting hormone release. Hormones produced enter the capillary bed and from there enter into the general circulation
What are the hormones of the posterior pituitary?
The hormones of the posterior pituitary are:
- ADH
- Oxytocin
What are the hormones of the anterior pituitary?
The hormones of the anterior pituitary are:
- Growth hormone
- Prolactin
- Thyroid stimulating hormone
- ACTH
- LH and FSH
What is the role of ADH?
More ADH means higher blood pressure and increased blood volume
What is the role of oxytocin?
In pregnant women it causes contractions in the uterine smooth muscle to assist in labour
In lactating females, it causes milk ejection by contraction of the smooth muscle in mammary gland tissue
In non-pregnant women it assists in the movement of sperm after sexual intercourse
In men the role isn’t precisely understood, but it’s thought to link to pair bonding and sperm motility
What controls the secretion of growth hormone?
Growth hormone releasing hormone and growth hormone inhibitory hormone are produced by the hypothalamus and control the secretion of growing hormone. This is typically in response to low blood glucose and other stressors
What is the role of growth hormone?
Growth hormone stimulates growth in most tissues, regulates metabolism and blood nutrient levels
Under secretion- dwarfism Over secretion (children)- giantism Over secretion (adults)- acromegaly
What controls the secretion of prolactin?
Prolactin secretion is controlled by the prolactin releasing hormone and prolactin inhibitory hormone produced by the hypothalamus
What is the role of prolactin?
Prolactin has an important effect in milk production in lactating females and enhanced progesterone following ovulation
The role in men hasn’t been identified
What controls the secretion of thyroid stimulating hormone?
The secretion of thyroid stimulating hormone is controlled by the thyroid releasing hormone from the hypothalamus to stimulate TSH release
What is the role of thyroid stimulating hormone?
Thyroid stimulating hormone causes the release of thyroid hormones from the thyroid gland
What controls the secretion of oxytocin?
Oxytocin is released when the uterus is stretched or cervix or nipples are stimulated while nursing
What controls the secretion of anti diuretic hormone?
ADH is released when blood pressure falls or when the blood becomes more concentrated. It targets the kidney causing it to retain water and reduce urine volume
What is the role of ACTH?
The release of ACTH causes a release of cortisol from the adrenal cortex and release of melanocyte stimulating hormone that causes increased skin pigmentation
What controls the secretion of leutinising hormone and follicle stimulating hormone?
The release of LH and FSH is stimulated by gonadotropin releasing hormones from the hypothalamus
What is the role of leutinising hormone and follicle stimulating hormone?
LH and FSH promote growth of the gonads (testes and ovaries and the production of sperm and ovocytes). They regulate reproduction with prolactin and control the production of reproductive hormones
Describe the shape and position of the thyroid gland:
The thyroid gland is a butterfly shaped tissue of two lobes, lateral to the trachea and just under the larynx
A narrow band of tissue connects the two ones across the anterior trachea
What hormones are produced by the thyroid?
The hormones produced by the thyroid are:
- Triiodothyronine T3 (10% of secretion)
- Tetraiodothyranine T4 (80%)
- Calcitonin (10%)
What controls the secretion of T3 T4 and calcitonin?
TRH from the hypothalamus and TSH from the anterior pituitary lead to the release of T3 and T4 from the thyroid into the bloodstream
How are T3 and T4 transported around the body?
T3 T4 are water insoluble hormones, meaning they need special proteins to carry them around the body to the target tissue. Here the hormones cross the cell membrane to bind to the intracellular receptor
What are the roles of T3 and T4?
T3 T4 act on almost all of the cells of the body
Their effects include:
1. Control of metabolism (increased metabolic action and temperature with increase T3/4)
- Regulation of normal growth in hormones (too little= hypothyroidism, weight gain. Too much= hyperthyroidism= weight loss)
Where is calcitonin secreted from?
Calcitonin is secreted from parafollicular cells within the thyroid tissue
What controls the secretion of calcitonin?
Parafollicular cells secrete calcitonin when blood calcium levels are high
What is the role of calcitonin?
Calcitonin is released when blood calcium levels are high. It reduces plasma calcium to maintain normal blood, which is very important to our health
Describe the location of the parathyroid gland:
The parathyroid gland is four small islands of cells embedded in the posterior thyroid tissue
What is the role of the parathyroid gland?
The parathyroid gland produces parathyroid hormone which regulates calcium levels in the blood by increasing plasma levels
Essentially, it does the opposite of calcitonin and increases the rate of formation of Vitamin D too
Where are the adrenal glands located?
The adrenal glands are located near the apex of the kidney
Describe the structure of the adrenal glands:
Each adrenal gland has an inner medulla and outer cortex
What hormones are secreted by the adrenal medulla?
The adrenal medulla secretes two hormones into the bloodstream:
- Adrenaline
- Noradrenaline
What are the roles of adrenaline and noradrenaline?
When released into the blood, adrenaline and noradrenaline had widespread effect on the body, by preparing us for fight or flight
What does our body do to prepare for fight or flight?
Preparation for fight or flight includes:
- An increase in blood glucose levels
- An increase in lipid breakdown
- An increase in heart rate
- An increase in force of contraction
- An increase in vasoconstriction to the skin, kidney and GI tract
- Vasodilation to the heart and skeletal muscles
What hormones are secreted by the adrenal cortex?
The adrenal cortex secretes three hormones:
- Mineralocorticoids (eg aldosterone)
- Glucocorticoids (eg cortisol)
- Androgens
What is the role of mineralocorticoids?
Mineralocorticoids (eg aldosterone) are secreted in response to low blood pressure. They cause the kidney to retain sodium and water to increase the blood volume and therefore pressurre
What is the role of glucocorticoids?
Glucocorticoids (eg cortisol) are produced in response to stress and has a mainly metabolic and anti-inflammatory effect
What is the role of androgens?
Androgens have a small effect on the development of secondary sexual characteristics in males
In females, androgens stimulated pubic and auxiliary hair growth and develop sex drive
Where is the pancreas located?
The pancreas is located between the stomach and duodenum
What is the role of the pancreas in the endocrine system?
The pancreas has endocrine value in that the islets of langerhans secrete hormones into the blood stream
What are the islets of langerhans made up of?
The islets of langerhans are mad up off:
- Alpha cells
- Beta cells
- Delta cells
What do alpha cells secrete?
Alpha cells in the islets of langerhans secrete glucagon to increase the breakdown of glucose
What to beta cells secrete?
Beta cells in the islets of langerhans secrete insulin to cause cells to increase their uptake of glucose and amino acids
What do delta cells secrete?
Delta cells in the islets of langerhans secrete somatostatin to inhibit insulin and glucagon secretions
What are the reproductive hormones?
The reproductive hormones are:
- GnRH
- Leutinising hormone
- Follicle stimulating hormone
- Testosterone
- Inhibit
- Oestrogen
- Progesterone
- Relaxin
Where is inhibin produced?
Inhibin is produced by some cells of the testes
What is the role of inhibin?
Inhibin provides feedback to the anterior pituitary and inhibits FSH production
Where is relaxin secreted from?
Relaxin is secreted by the ovaries during pregnancy
What is the role of relaxin?
Relaxin is secreted during pregnancy to increase the flexibility of the pubic symphysis and dilate the cervix to assist in delivering the baby
Where is testosterone produced?
Testosterone is produced by males in the testes
What is the role of testosterone?
Testosterone stimulates the development of male reproductive structures, secondary sexual characteristics/ behaviours, causes the growth of the larynx and reduces tension in the vocal cords (deeper voice)
What are oestrogen and progesterone produced by?
Oestrogen and progesterone are produced by the ovaries under the influence of LH and FSH
What are the roles of oestrogen and progesterone?
Oestrogen and progesterone control the female reproductive cycle, prepare the mammary glands for lactation, maintain pregnancy, develop the female reproductive organs and develops secondary sexual characteristics
During the first trimester of pregnancy, the placenta secretes an LH like hormone to maintain the pregnancy. Throughout, the ovaries and placenta produce increasing amounts of O and P to help maintain the pregnancy
