Endocrine System Flashcards
(24 cards)
Endocrine system
Cellular communication is essential to maintain homeostasis
There are 4 main types of communication we need to consider
Direct signaling
Single cell contact
Gap junction (animals) and plasmodesmata (plants)
Tiny channe;s that direct;y connect neighbouring cells
Signalling molecules diffuse between the two
Two cells may bind to one another because they carry complementary proteins on their surfaces
• This interaction changes the shape of one or both proteins, transmitting a signal
• Important in the immune system
• immune cells recognize “self” cells (the body’s own cells) and cells infected by pathogens
Autocrine Signaling
Cells respond to molecule produced by themselves
allows cell to alter its own extra cellular environment, which in turn affects the way the cell functions
Important for growth - Growth Factors
Paracrine signalling
Cell affects the behaviour of another cell by secreting chemicals into the common intercellular space
Secreted molecules affects only target cells in the proximity of the signalling cell
Synaptic Signalling
Nervous syst3em
Highly specific and localised type of paracrine signalling between two nerve cells or nerves and muscle cell
Neurotransmitters
Endocrine Signalling
Hormone secreted int the bloodstream by endocrine gland
Distant target reached by bloodstream
Endocrine system
Co-ordinated, along with nervous system,
- water and ion balance
- metabolism
- nutrient absorption
- reproduction
Endocrine system 2
The second coordinating and integrating system of the body.
• Nervous System – electrical signals – fast action – short rapid communication
• Endocrine System – chemical signals – slower action – more prolonged responses
• Endocrine System - complex network of glands that synthesis and release hormones into the
bloodstream to control and coordinate:
✓ Maintenance of homeostasis – response to injury, stress and mood
✓ Control, storage and utilisation of energy – glucose control by the endocrine portion of
the pancreas
✓ Growth – maturation of reproductive systems & embryo development.
✓ Response to environmental stimuli.
• Glands are clusters of epithelial cells specialised for a secretory function (they synthesise
and secrete ‘products’)
• Exocrine glands secrete products into ducts that carry them outside the body (including into
lumens) e.g. sweat, oil, mucus, digestive
• Endocrine glands secrete products (hormones) into interstitial fluid surrounding secretory
cells. Hormones diffuse into blood, blood carries them to their targets
Endocrine system 3
The second coordinating and integrating system of the body.
• Nervous System – electrical signals – fast action – short rapid communication
• Endocrine System – chemical signals – slower action – more prolonged responses
• Endocrine System - complex network of glands that synthesis and release hormones into the
bloodstream to control and coordinate:
✓ Maintenance of homeostasis – response to injury, stress and mood
✓ Control, storage and utilisation of energy – glucose control by the endocrine portion of
the pancreas
✓ Growth – maturation of reproductive systems & embryo development.
✓ Response to environmental stimuli.
• Glands are clusters of epithelial cells specialised for a secretory function (they synthesise
and secrete ‘products’)
• Exocrine glands secrete products into ducts that carry them outside the body (including into
lumens) e.g. sweat, oil, mucus, digestive
• Endocrine glands secrete products (hormones) into interstitial fluid surrounding secretory cells. Hormones diffuse into blood, blood carries them to their targets
Organs of the endocrine system
Pineal gland
Pituitary gland
Parathyroid gland
Thyroid gland d
Thymus
Adrenal gland
Partial endocrine glands - contain endocrine tissue
Hypothalamus
Pancreas
Kidneys
Testes/Ovarues
Hormones
Specific chemical messenger molecules that regulate the activity of cells or organs in the body
Synthesised and secreted by cells in endocrine glands.
Effects may be slow to appear but typically last for days
Alter operations of target cells in a variety of ways:
– Stimulate synthesis of an enzyme or structural protein NOT already present in the
cytoplasm
– Via activation of appropriate genes in cell nucleus
– Increase / decrease the rate of synthesis of a particular enzyme or other protein
– By changing rate of transcription / translation
– Turn an existing enzyme / membrane channel ‘on’ or ‘off’
– By changing its structure / shape
• Therefore can modify the physical structure or biochemical properties of the target cells
3 main classes of hormone
Amino acid derivatives
- Thyroxine and adrenaline
- Relatively small
- Most derivative of tyrosine
Peptides hormones
- Thyroid stimulation hormone, oxytocin, insulin
- Formed from chain of amino acids.
- Synthesied as prohomones
Steroid hormones
- Sex hormones - progesterone, tostesterone, oestrogen
- Derived from cholesterol
- Release from male & female reproductive organs
Secretion and distribution of hormones
• Hormones may circulate freely or are bound to transport proteins
– Free hormones are rapidly removed from bloodstream
• Amine (catecholamines) & peptide hormones
– These are generally water soluble & dissolved in the plasma
– Receptors are in cell membrane or target cells
• Thyroid & steroid hormones
• Circulate in blood largely bound to plasma proteins
• N.B. Only free hormone concentration is physiologically
important
• Lipid soluble - cross membrane & bind to receptors in the cytoplasm or nucleus
- Activate or inactivate specific genes
Endocrine Structures in the Diencephalon
Between brain stem and cerebrum
Two main sections:
Hypothalamus & thalamus
Also has two endocrine structures:
pituitary & pineal glands
Hypothalamus - Provides the highest level of endocrine
control.
• Linked to the pituitary gland through a network of
blood vessels and neurons
• Controls the secretory activities of endocrine cells in
pituitary gland by producing releasing and inhibiting
hormones.
• Indirectly controls the functions of the thyroid gland,
adrenal glands, and reproductive organs and
influences growth, fluid balance, and milk production
Note: hypothalamus involved in the non-endocrine function of temperature regulation, regulation of the autonomic nervous system and the control of appetite
Pituitary
Hypothalamus secretes releasing hormones and inhibiting hormones
• Hypothalamus is connected to and communicates with your anterior lobe through a network of
blood vessels.
• Hormones generated in hypothalamus travel in hypothalamic neurons (hypothalamic neurons (hypothalamic neurosecretory cells) directly to the posterior pituitary
Vasopressin/Antidiuretic Hormone (ADH)
Increase water reabsorption from urine in response to dehydration.
Plasma osmolality measures the body’s electrolyte–water balance.
Osmoreceptors regulate sodium and water balance in a manner that maintains the osmotic pressure of the
extracellular fluid (ECF) near an ideal set point.
Osmoreceptors respond
to solute concentrations of body fluids
Note: Significant reductions in arterial blood pressure and blood volume can also stimulate ADH secretion - initiated by arterial baroreceptors
Negative feedback by hormones
- The anterior pituitary gland secrete a tropic
hormone, which travels in the blood to the
target endocrine cell - The hormone from the target endocrine cell
travels to its target - The hormone from the target endocrine cell
also has a negative feedback effect on the
anterior pituitary and hypothalamus and
decreases secretion of the tropic hormone
Pineal gland
René Descartes (*1596) believed the
pineal gland to be the “principal seat
of the soul”.
• Structure in brain that does not occur
in duplicate (both hemispheres)
• Secretes melatonin
• Contributes to setting biological clock
(secretion changes in response to
visual input from eyes = circadian
rhythm)
Thyroid gland
• Located below the Larynx
• Regulates bioenergetics, helps maintain blood pressure, heart rate and muscle tone. It regulates digestive and reproductive functions.
• Thyroid hormone (Thyroxine (T4) and Triiodothyronine (T3) — collectively make up thyroid hormone)
• Thyroid hormone has a negative feedback loop regulation on hypothalamus and anterior pituitary
• If the level of thyroid hormone in blood drops, the hypothalamus secretes the TRH ( thyrotroponin releasing hormone).
• TRH causes the anterior pituitary to secrete TSH, thyroid- stimulating hormone.
• TSH in turn stimulates the thyroid gland that secretes the thyroid hormones: -Triiodothyronine (T3) -Thyroxine (T4)
Thyroid deregulation
Hyperthyroidism
- Excess of T3 and T4 secreted
- increases basal metabolic rate, excess sweating, muscle weakness, increased body temp irritability.
Hypothyroidism
- Under secretion of T3 and T4
- Iodine deficiency
-Slow heart rate, low body temp, weight gain, intolerance to cold
Pancreas
• Located in the curve of the duodenum
• Pancreas acts as an exocrine gland (digestion) and as an endocrine gland (blood glucose)
• Glucose homeostasis relies on the antagonistic effects of two hormones:
➢ Alpha cells: glucagon (promotes the release of glucose into the blood from energy stores).
➢ Beta cells: insulin (triggers the uptake of glucose from the blood into body cells, < blood glucose concentration)
Glucose stored in liver as Glycogen
Glucagon breaks down glycogen to release glucose back into the bloodstream
Control of Blood Glucose – Islets of Langerhans
• Islets of Langerhans – endocrine part of the pancreas.
• Contain four main types of peptide-secreting cells:
• β (or B) cells secrete insulin.
• α (or A) cells secrete glucagon. [opposes insulin, increasing blood glucose]
• δ (or D) cells secrete somatostatin [inhibits secretion of insulin and of glucagon].
• PP cells secrete pancreatic polypeptide (PP). [implicated in control of food intake
Diabetes
Type 1 Type 2
Insulin Resistance
Genetics
Obesity
Hyperglycaemia
Autoimmune destruction of beta cells
Environmental trigger
Diabetes
• Diabetes mellitus can be defined as a chronic metabolic disorder characterised by a
high blood glucose concentration – hyperglycaemia (fasting plasma glucose >
7.0 mmol/L)
• Blood glucose rise to a dangerous level
Adrenal glands
Play a major role in the body’s response to stress
The glands are located in top of each kidney
Adrenal glands have two parts
- Adrenal cortex
- Adrenal medulla
