Endocrine Flashcards
Define humoral stimuli
Stimuli that trigger hormone release in response to changing blood levels of certain critical ions or nutrients.
Ex: parathyroid hormones in response to blood calcium levels
Define neural stimuli
Stimuli that trigger hormone release in response to neural input, such as sympathetic activation of adrenal medullary glands to secrete adrenaline and noradrenaline
Define hormonal stimuli
Hormonal stimuli themselves can trigger another hormone to be released, such as hormones released from the hypothalamus that regulate the release of other hormones from the anterior pituitary lobe
Name the effects hormones have
- Alter plasma mb permeability
- Stimulates synthesis of enzymes
- Activates/deactivates enzymes
- Increases secretory activity
- Stimulates mitosis
Define exocrine glands
A ducted system carrying non-hormonal substances such as sweat and saliva to a mb substance
Define endocrine glands
A ductless system delivering hormones into surrounding tissue fluid near rich vascular and lymphatic drainage for distribution
Describe the relationship the hypothalamus has in regards to the pituitary gland
The hypothalamus releases and inhibits hormones transported by a portal system to the anterior lobe of the pituitary gland
The hypothalamus manufactures and delivers anti diuretic hormone (ADH) and oxytocin via axonal transport to the posterior lobe of the pituitary gland
Define and describe neurohypophysis
The posterior tube of the pituitary gland originated as a down growth hypothalamic tissue and it maintains its neural connection with the hypothalamus via the hypothalamic-hypohyseal tract, which runs inferiorly through the infundibulum.
The posterior lobe and the infundibulum together are known as the neurohypophysis. Oxytocin and ADH are produced in the hypothalamus and delivered via axonal support to the neurohypophysis.
Define and describe adenohypophysis
The anterior lobe of the pituitary originates from epithelial tissue and is attached to the anterior to the posterior lobe of the pituitary. Bc of its granular structure, the anterior lobe is referred to as the adenohypophysis.
What does the hypothalamic nuclei synthesize?
Oxytocin and ADH. These hormones are transported down the axons of the hypothalamic-hypophyseal tract where they are stored in the axon terminals in the posterior periphery.
What is the function of ADH?
Influences water balance, blood pressure and osmolarity of body fluids. It is stimulated by a drop in blood pressure, or increase in plasma osmolarity.
What is the function of oxytocin?
It is a hormone that stimulates smooth muscle contraction in the breasts and uterus. The release is stimulated by onset of labour or a baby sucking the breasts during lactation.
What is the role of hypothalamic osmoreceptors?
They monitor solute concentration of the blood and receive signals from barorrceptors regarding blood pressure changes
How does osmolarity relate to ADH?
ADH is an anti diuretic, meaning it prevents or inhibits urine formation.
So ADH is a hormone that prevents large swings in water balance in order to prevent dehydration or water overload.
If high osmolarity (high concentration of solute in the blood), such as following excessive perspiration, the hypothalamus is alerted to stimulate the release of ADH.
Once released from the posterior pituitary gland, ADH targets the kidney which responds by increasing water reabsorption from the forming urine and returning it to the bloodstream.
Low osmolarity, or low concentration of solutes in the blood, results in less ADH released, we no longer need to retain water and we experience an increase in water loss from the kidney in the form of increased urination
Describe the physiological effects of oxytocin
Oxytocin is released from the posterior pituitary. It is a strong stimulant of uterine contraction and is secreted in response to stretch of cervix during labour, and is also used to induce labour.
It is secreted in response to a baby sucking the breast, and the release of oxytocin triggers milk ejection during lactation and this is known as a letdown reflect. It has a role in bonding between partners and parental bonding with infants.
Define tropic hormone
Hormones that control the development, maintenance and secretin from a variety of glands in the body. Tropic hormones directly act on another endocrine gland.
Define non-tropic hormone
Hormones that directly affect non-endocrine target tissues.
Describe growth hormone
It is a tissue building hormone that has both metabolic and growth-promoting actions.
It stimulates the liver to produce insulin-like growth factors (IGFs or somatomedins) which act as hormones on target tissues.
Name the two antagonistic hypothalamic hormones that regulate ADH
- Growth hormone releasing hormone (GHRH)
- Growth hormone inhibiting hormone (GHIH)
The balance between the two are regulated by many factors such as sleep, stress, glucose levels
Describe thyroid releasing hormone (TSH)
TSH stimulates normal development and secretory activity of the thyroid gland
Secretion of TSH is triggered by thyrotropin releasing hormone, which is released by the hypothalamus
Rising blood levels of thyroid hormones feedback into the anterior pituitary and the hypothalamus to block the release of thyroid stimulating hormone
Describe adrenocorticotropic hormone (ACTH)
ACTH stimulates the adrenal cortex to release corticosteroids such as glucocorticoids. Glucocorticoids (cortisol) help the body resist stress.
Secretion of ACTH is triggered by corticotropin releasing hormone. Secretion of ACTH occurs in a daily rhythm occurring in the morning before waking.
The release of corticotropin releasing hormone from the hypothalamus is triggered by fever, hypoglycaemia and stressors.
Describe follicle-stimulating hormone (FSH) and luteinising hormone (LH)
These two hormones are gonadotropins and their job is to regulate function of the gonads, the ovaries and testes.
Secretion is triggered by the hypothalamic gonadotropin-releasing hormone during and after puberty.
Describe follicle-stimulating hormone (FSH)
FSH stimulates gamete production in both sexes, that is stimulates egg and sperm production
Describe the function of luteinising hormone
It promotes the production of gonadal hormones. It triggers ovulation and promotes the synthesis and release of estrogen and progesterone.
In makes it stimulates the testes to produce testosterone.
Describe the role of prolactin
It’s main role is to stimulate milk production in females. Prolactin levels rise and fall with estrogen blood levels.
Sucking stimulates prolactin release, encouraging milk production.
Prolactin is controlled by prolactin-inhibiting hormone (dopamine) (PIH). PIH inhibits release of prolactin.
Describe the thyroid gland
It is the largest endocrine gland in the body. It consists of 2 lateral lobes, connected by the isthmus.
The thyroid gland is composed of follicles, and the walls of the follicles are made up of follicular cells.
Follicular cells produce thyroglobilin which is the precursor to thyroid hormone.
Describe thyroid hormone
It is the major metabolic hormone of the body. It stimulates enzymes concerned with glucose oxidation which increases basal metabolic rate. It increases lipolysis, and TH is important in producing body heat (i.e. thermogenesis or calorigenic effect).
Thyroid hormone increases the number of adrenergic receptors in the blood vessels and enhances sympathetic NS activity, resulting in increased heart rate and cardiac contractility.
Thyroid hormone is imb in regulating tissue growth and development, skeletal and NS development and maturation for reproductive capabilities.
Describe how the synthesis and release of thyroid hormone is regulated
When increase in metabolic rate is required, thyrotropin-releasing hormone (TRH) is released from the hypothalamus.
TRH stimulates the release of thyroid stimulating hormone from the anterior pituitary lobe.
Thyroid stimulating hormone stimulates the synthesis and release of thyroid hormone from the thyroid gland
How is hypothyroidism caused?
It is the deficiency of thyroid hormone. It is caused by:
- Iodine deficiency
- Damage to the thyroid hormone
- After surgical removal of the thyroid
Define myxoedema
It is hypothyroidism in adults, and is a mucus swelling.
Patients have a decrease in their metabolic rate, weight gain, puffy skin and slow reflexes.
Define cretinism
This is children with severe hypothyroidism due to an iodine deficiency.
These patients are dwarfed and intellectually handicapped, and have a thick tongue and neck.
Describe the parathyroid glands
They are 4 tiny glands embedded in the posterior aspect of the thyroid gland
Small densely packed, parathyroid chief glands synthesize and secrete parathyroid hormone.
Parathyroid hormone is involved in regulating calcium balance in the blood
Describe the role of PTH in calcium homeostasis
PTH stimulates osteoclasts and inhibits osteoblasts.
PTH enhances resorption of calcium by the kidneys, while promoting excretion of phosphate by the kidneys.
PTH promotes activation of vitamin D, thus increasing absorption of calcium by the intestinal mucosal cells.
Rising blood calcium levels inhibit PTH release
Falling levels of blood calcium stimulate PTH release
Define calcitonin and it’s function
It is a hormone produced by the parafollicular cells.
It is released in response to rising blood calcium levels and has a role in calcium homeostasis by lower blood calcium levels, thus acting as an antagonist to PTH.
Calcitonin inhibits osteoclasts activity, decreases bone resorption and decreases calcium release from the bone matrix and stimulates calcium uptake.
Describe the function of the adrenal glands
The adrenal glands are a pyramid shaped organs that attach to the posterior of the kidneys
It has 2 glands in 1: the medulla and cortex
Describe the adrenal medulla
It is derived from nervous tissue (sympathetic NS) and secretes hormones (adrenaline and noradrenaline) not neurotransmitters.
Describe function of the adrenal cortex
It is the synthesis and secretion of steroid hormones (corticosteroids) such as mineralocorticoids, glucocorticoids and sex hormones
Describe the structure of the adrenal cortex
The outermost layer is the zona glomerulosa
The middle layer is the zona fasciculata
The innermost layer is the zona reticularis
Describe the glucocorticoids and provide and example
Produced in the adrenal cortex. And is released from the fasciculata and the reticularis cells in the adrenal cortex to influence energy metabolism of body cells and to help us resist stress.
Cortisol increases the rate of glucose stored as glycogen
Describe mineralocorticoids and provide an example
Produced in the zona glomerulosa, and is responsible for regulating the electrolyte concentration in extra cellular fluids, such as sodium and potassium.
Aldosterone regulates calcium and potassium. And it maintains sodium balance by reducing the urinary excretion of calcium.
Describe the pancreas
Located in the epigastric and left hypochondriac regions of the abdominal cavity and superior to the large intestine.
Possesses both endo and exocrine cells.
Describe how the pancreas has an exocrine function
Acinar cells form the majority of the gland and responsible for producing an enzyme rich pancreatic juice used for digestion
Describe how the pancreas has an endocrine function
Scattered amongst the acinar cells are pancreatic islets which are known as islets of langerhans, and these produce pancreatic hormones.
Describe the two cell types the pancreatic islets produce
- Alpha cells that secrete glucagon to increase blood glucose
- Beta cells will high secrete insulin to decrease blood glucose
Describe the location of the pineal gland
It is a small gland that hangs from the roof of the 3rd ventricle and is apart of the epithalamus in the diecephalon
Describe the function of the pineal gland
It secretes melatonin, which maintains daily circadian cycles such as sleep, sleep and appetite.
The suprachiasmatic nucleus inhibits melatonin release through activation of GABA projections to the paraventricular nucleus.
The paraventricular nucleus is stimulated to activate sympathetic neurons to the superior cervical ganglion in the neck, which synapse with neurons that stimulate the pineal gland to release melatonin.
Describe the location of the thymus
Located deep in the sternum in the anterior mediastinum. It is a lobulated gland that is large in children but shrinks in adults.
Describe the function of the thymus
Produces the peptide hormone for the development of the T lymphocytes, which is important in our immune response.
Describe the function of the female gonads
The ovaries in the abdominopelvic cavity produce estrogen and progesterone.
Estrogens are used for the maturation of the reproductive organs and together with progesterone, stimulate breast development and changes in menstruation.
Describe the function of the male gonads
The testes located in the scrotum and produce testosterone. And is necessary for sperm production, growth of adam’s Apple, deeper voice.
Describe what hormone the heart produces and it’s function
Produced atrial natriuretic peptide (ANP), which reduces blood sodium concentration in the ECF, thus reducing blood volume and blood pressure.
Describe the hormones the gastrointestinal tract produces and the function
Produced gastrin, cholecystokinin and secretin.
Gastrin - released from stomach in response to food and stimulates glands to produces HCl
Cholecystokinin and secretin - secreted by small intestine in response to food and stimulates pancreas to release digestive juices
Describe the hormone the placenta produces and it’s function
Produces human chorionic gonadotropin which influences the course of pregnancy and maintains the corpus luteum progesterone production during the first 3 months of pregnancy
Describe the hormone the kidneys produce and it’s function
Produces erythropoietin which signals to the bone marrow to increase red blood cell production
Also produces renin
Describe the hormone the skin produces and it’s function
Produced cholecalciferol which is the precursor to vitamin D, which stimulates intestinal calcium absorption
Describe the hormone that the adipose tissue produces and it’s function
Produces leptin which acts as an appetite suppressant and also stimulates energy expenditure
