Introduction to the Endocrine System Flashcards
What are the 3 points on the Endocrine system verses the Nervous system?
- 2 major communication systems which regulate activities of the body and maintain homeostasis
- Interact to co-ordinate activities of different organs and tissues in response to physiological needs
- Endocrine is linked to the external environment via the nervous system so can be affected by external conditions
Give 3 differences between nervous system and endocrine systems
- Nervous system is always working but endocrine often functions intermittently
- Nervous system is discrete and localised but endocrine exert diffuse control
- Nervous system has rapid control but endocrine is often prolonged control
Explain the general mechanism of the endocrine system
- Stimulus activated endocrine cell (stimulus is specific to each endocrine gland)
- Endocrine cell releases hormone into blood or intracellular space (hormones rapidly cleared from the circulation by liver
- The hormone targets the tissue and this leads to negative feedback (the incoming stimulus is reduced)
What are the 4 functions of hormones in the body?
- Development (proliferation, differentiation, organogenesis)
- Metabolism (carbohydrate, energy storage, metabolic rate, temperature)
- Reproduction (sexual maturation and behaviour, maintenance of pregnancy, lactation)
- Fluid balance (water balance, salt levels, blood volume, pressure)
List the 6 endocrine glands
- Pituitary (anterior and posterior)
- Thyroid
- Parathyroids
- Islets of langerhans
- Adrenals
- Gonads (produces male and female gametes)
What tissues of the body secrete hormones and which hormones?
Kidney = erythropoietin (production of red blood cells)
Heart = atrial natriuretic peptide (Na excretion by kidneys increases to decrease blood pressure)
Vascular endothelium = blood clotting factors
Gut cells = gastrin, secretin
Adipocytes = leptin (suppresses appetite)
Placenta = lactose, hCG
Thymus = thymosins
Explain the difference between the endocrine mechanism and the neuroendocrine one
Endocrine - hormones released from endocrine cell into blood
Neuroendocrine - hormone released from nerve cell into blood
Explain neuroendocrine secretion
Secretory Neurons have specialised nerve-endings that store hormones within vesicles.
Generation of action potentials in these neurone causes the hormones to be released into nearby capillaries.
e.g. in hypothalamus, posterior pituitary, adrenal medulla
What do the different biochemical structures of hormones determine?
- the mechanism of action at the target cell
- how the hormone is carries in the blood
- the circulating half-life
What are the 3 main groups of hormones?
PROTEINS
STERIODS
AMINES
Give the 3 types of protein hormones
- Small peptides
- ADH (9 amino acids)
- TRH (3 amino acids) - Long chain proteins
- e.g. GH and insulin - Glycoproteins
- LH
How do the peptide hormones work?
- Synthesis by DNA transcription and translation
- Mostly synthesised first as large preproxhormones, then cleaved by proteolytic enzymes to form prohormones
- Prohormones stored in cell are granules in secretory vesicles
- Release of active hormone by exocytosis stimulated by increase in cytosolic calcium
- After release, peptide hormones diffuse into ‘leaky’ capillaries
- Often circulate in blood unbound because water-soluble, so have short half-lives
- All hormones of hypothalamus, pituitary, parathyroids, GI tract, pancreas
How do steroid hormones structure and function?
Where are they produced?
How do they circulate?
How do they enter the membrane?
All structures bases on three 6 carbon rings and one 5 carbon ring.
Fat soluble lipids derived from cholesterol.
Synthesised in mitochondria and smooth ER.
Not stored in gland, so hormone release is dependent on rate of synthesis.
Able to diffuse across plasma membrane.
Circulate in blood bound to proteins e.g. albumin, therefore have long half-lives.
Produced by adrenal glands.
How do amines hormones structure and function?
Where are they produced?
How do they circulate?
How do they enter the membrane?
They are modified amino acids, derived from tyrosine.
Thyroid hormones:
- Lipid soluble, can cross cell membranes
- Circulate in blood bound to proteins, have long half-lives
- Stored in thyroid gland bound to thryoglobulin
Catecholamines:
- Water soluble, do not cross cell membranes
- Circulate unbound in blood, have short half-lifes
- Stores intracellularly in secretory granules e.g. adrenaline
Give the details on Eicosanoids
Local chemical messengers that exert a wide variety of effects in may different organs and tissues.
Autocrine or paracrine activity.
Derived from arachidonic acid (fatty acid present in plasma membrane phospholipids).
Effect of prostagladins include:
- Immune system: promotor inflammatory process
- Reproductive system: pray role in ovulation
- Digestive system: inhibit gastric secretion
What cells tend to secrete proteins&catecholamines and which tend to secrete steroids &thyroid hormones?
- Proteins and catecholamines
- Steroids and thyroid hormones
Compare steroid&thyroid hormones with peptide&catecholamine
Steroid&thyroid hormones:
- Mainly bound to proteins e.g. albumin in blood, longer half life
- Receptor on the nucleus or intracellular cytoplasm
- They alter gene transcription
Peptide&catecholamine hormones:
- Carried in blood dissolved in plasma, short half-life
- Receptor on cell surface, plasma membrane
- Works by second messengers to change enzyme activity
What are the 4 controls of hormone secretion?
- Changes in plasma concentration of mineral ions e.g sodium, calcium, potassium
- Changes in plasma concentration of organic nutrients e.g. glucose
- Neurotransmitters releases from neurones contacting endocrine cells
- Another upstream hormone acting on the endocrine cell
Explain the chemical structure on insulin
- Formed from a pro-peptide called pro insulin
- Insulin A-chain has 21 amino acids, B chain has 30 amino acids
- Chains are connected by 2 disulphide bonds
- Insulin is highly conserved between species
Give the details on type 1 and type 2 diabetes
Type 1 diabetes
Typically occurs in children and young adults
• Islet β-cell destruction is ongoing and symptoms develop rapidly when there is insufficient insulin to regulate blood glucose levels.
• Glycosuria occurs as excess glucose is lost in the urine.
• This is accompanied by muscle wasting as protein is broken down to be used as fuel.
- Requires insulin replacement as b-cells are the only cells that make this hormone.
Usually occurs in adults (but becoming more common in children)
• Type 2 diabetes is associated with obesity and a sedentary lifestyle.
• Hormones secreted by adipocytes make cells less sensitive to insulin.
• b-cells work harder to overcome this insulin resistance and eventually don’t work properly, so insulin secretion is insufficient.
• Usually doesn’t require insulin replacement therapy, but 60% of people with T2D require insulin within 10 years.
Why does diabetes lead to periodontal disease?
Fatty plaques are laid down in aorta reducing blood flow. Slows nutrients and weakening the resistance of gym and bone tissue to infection.
High blood sugar then helps bacteria to grow and leads to this disease.
Give some info on the anatomy of the pituitary gland
• Also known as the hypothysis • Weighs less than 1g in humans • Comprised of two main lobes • Adenohypohysis / anterior lobe • Glandular • Neurohypohysis / posterior lobe • Neuronal processes from SON and PVN -Also the intermediate lobe -ProducesMSH • Not in adult humans
Formed from 2 embryologically distinct ectodermal tissues.
a) an invagination of the forebrain forming the posterior lobe
b) outgrowth of buccal cavity (Rathke’s pouch) forming the anterior lobe
Explain the embryonic development of the pituitary
Invagination of hypothalamus and the Rathke’s pouch form.
The two lobes then come together and form the pituitary.
Give details on the posterior pituitary
The posterior pituitary is controlled directed by neuronal projections from the brain.
It consists mainly of axons of certain hypothalamic neurones, which reach down and form a bundle behind the anterior pituitary.
It also forms the pituitary stalk, which appears to suspend the whole pituitary gland from the hypothalamus.
Controlled directly by neuronal projections from the brain.
What hormones come from the posterior and anterior pituitary?
Hormones from posterior pituitary: Vasopressin Oxytocin Growth hormone LH Thyroid hormone FSH
Hormones from anterior pituitary: Growth hormone LH FSH Adrenocorticoid hormone Cortisol
How does neural stimuli get from the hypothalamus to the posterior pituitary?
Via axons which travel downwards.
The axons terminals in close association with blood vessels.
Synthesis of hormones occurs in cell bodies which is transported down the axons and stored in nerve terminals and then released into blood.
Explain the actions of the posterior pituitary gland with ADH
With oxytocin?
ADH secretion is stimulated directly by increased plasma osmolality (usually due to a rise in sodium plasma).
This ADH increases water resorption in the kidney and so decreased osmolality and increases blood volume and blood pressure.
Stretching of cervix during birth simulates this secretion. Oxytocin increases uterine contractions and stimulates milk ejection.
What are the 5 endocrine cell types?
- Gonadotroph cells
- Corticotrophs cells
- Somatotroph cells
- Lactotroph cells
- Thyrotroph cells
What are the 6 hormones that the anterior pituitary releases?
Thyroid stimulating hormone (TSH), Adrenocorticotrophic hormone (ACTH), Luteinising hormone (LH) and Follicle Stimulating Hormone (FSH) are trophic (stimulatory) to other specific endocrine glands. All released from anterior pituitary. Growth Hormone (GH) has been shown to exert its growth-promoting effects by stimulating the release of liver hormones, the somatomedins, it too can be categorized as a trophic hormone. Prolactin (PRL) is the only one which does not stimulate production or secretion of another downstream hormone.
How is the anterior pituitary controlled?
None of the anterior pituitary hormones are secreted at a constant rate.
Though each has a unique control system, there are common regulatory features.
The 2 main features are:
• Hypothalamic hypophysiotrophic hormones.
• Feedback by target gland hormones.
Where are hypothalamic hypophysiotropic hormones released?
From the pituitary portal system from nerve terminals in the median eminence of the hypothalamus.
Stimulate the releases of specific hormones from the anterior pituitary.
What allows the endocrine system to maintain homeostasis?
Negative feedback
Take-home messages?
- Hormones can be present in low concentrations yet have dramatic effects
- Widespread in body but only affect specific target organs
- The endocrine system uses feedback to ensure long-lasting homeostasis
- The pituitary is essential as the interface between the hypothalamus and the many target endocrine organs it controls
- The hypothalamus and pituitary also regulate endocrine systems thorough acting as an important point of feedback
