Week 4 Lecture 12: Endocrine System
Hormones
Molecular signals
Released by specific cell types
Influence other cells
A system that includes a variety of cells, tissues and organs that produce hormonal molecular signals
The study of hormones is known as endocrinology
Three different groups
1. Peptides or proteins
2. Steroid hormones (lipid hormones)
3. Amines
Major group
Water soluble (hydrophilic)
Easily transported in blood
Packaged within vesicles in cells
Secreted via exocytosis
e.g. insulin
Synthesised from cholesterol, a steroid
Lipid soluble (lipophilic)
Can pass through cell membranes
NOT packaged into vesicles
Secretion regulated by regulating synthesis
Diffuse out of cells
Steroid hormones are bound to carrier molecules in blood
e.g. testosterone
Because steroid ligands are lipophilic, they are hydrophobic and need the hydrophilic carrier molecule to transport them
This is how synthesis is limited
Mostly synthesised from tyrosine, an essential amino acid
Can be water soluble OR lipid soluble (hydrophilic or lipophilic)
Therefore, mode of action differs
e.g. epinephrine
e.g. thyroxine
Hormone receptors (same as Lecture 11)
Three different kinds
1. Membrane bound
2. Cytoplasmic
3. Nuclear
Binded to a protein/amine
Binded to a steroid/amine
Usually a steroid-receptor complex that travels through the nuclear pore into the nuclear #
This initiates or inhibits RNA transcription
Causes a signal transduction cascade
Activation of an enzyme in cytoplasm
Activate another molecule to stimulate RNA transcription in nucleus
Synthesis of a product via cytoplasmic enzymes
Steroid hormones mostly act in the nucleus
Regulating a number of genes (20 or 30)
Short-term effect
e.g. epinephrine stimulate glucose synthesis
Long-term effect
Effects up to an hour, a few hours or even more
Glands
Hormones are in glands
Glands are tissue
Epithelial tissue
Connective tissue
Two types of glands in the body
1. Endocrine
2. Exocrine
Aggregation/collection of cells that secrete hormones directly into the blood
Secrete enzymes (usually) via ducts to an external environment (target tissue/organ)
Often to an external surface (but not necessarily skin – can be the gut for example)
e.g. exocrine pancreas secretes enzymes and bicarbonate via a duct to the duodenum 🚩
e.g. estrogen
e.g. aldosterone
e.g. cortisol
e.g. endocrine pancreas secretes insulin and glucagon directly into blood
e.g. salivary glands secrete amylases during mechanical digestion
e.g. lacrimal glands
e.g. gallbladder
Types of endocrine glands in humans, their hormones and their target tissue (or function)
Pineal gland
Hypothalamus
Pituitary gland (raisin-sized; releases eight hormones)
Anterior pituitary
Posterior pituitary
Parathyroid glands
Four small glands behind the thyroid gland
Release parathyroid hormone to increase calcium levels in the blood
Thyroid stimulating hormone (TSH) 🚩
Follicle stimulating hormone (FSH)
Luteinising hormone (LH)
Adrenocorticotropic hormone (ACTH)
Growth hormone (GH)
Prolactin
Oxytocin
Antidiuretic hormone (ADH)
Melatonin
Thyroid gland
Thyroxine 🚩
Calcitonin
Thymus gland
Adrenal glands
Two, one on top of each kidney
Components of an adrenal gland (synthesise and store hormones)
Inner medulla
Outer cortex
Pancreas
Insulin
Glucagon
Decreases blood glucose levels
Increases blood glucose levels
Gonads (release sex hormones)
Ovaries
Testes
Estrogen
Progesterone
Testosterone
Releasing and inhibiting hormones that directly stimulate or inhibit the anterior pituitary gland to secrete its hormones, via the portal vessels
Thyroid gland
Ovaries
Regulates release of sex hormones (steroids) in the gonads
Adrenal glands
Most cells
Breast cells
Uterine muscles
Kidney tubules
Other types of endocrine glands that secrete hormones
Adipose tissue
Heart
Stomach
Skin
Liver
Allows the egg to ovulate in the ovaries
Stimulates breast milk in women
Sexual response in men
Effect on oligodendrocytes (glial cells) in brain
Testes
Testes
Uterine contraction to prepare the uterus for delivery, and during delivery
Regulates the amount of water in blood
Aldosterone
Cortisol
Epinephrine 🚩
Norepinephrine
These hormones from the inner medulla are amines which are NOT lipid soluble
The hormones are stored in vesicles in cells of the inner medulla
The brain detects danger and signals the adrenal glands to release epinephrine and norepinephrine in a stressful situation
This tells the body to act – i.e. fight or flight response
Situations
Anxiety before an exam
Running away from a dangerous situation (e.g. poisonous snake)
The signal traduction pathway can be initiated in minutes or even seconds
The response is very rapid as the adrenal medulla is regulated by the sympathetic nervous system (for all fight-or-flight situations)
Stress
Actions
Heart beats faster
Blood pressure increase
Breathing becomes quicker and shallow
Digestive system slows down drastically
Blood flow diverted to skeletal an cardiac muscles
Liver cells break down glycogen and secrete glucose for energy
Enzyme cascade stops glycogen production
Fat cells release fatty acids for energy
Target cells for E and NE
Circulatory system
Muscles
Liver and fat cells
aka. Adrenaline
aka. Noradrenaline
Usually 1st indication of stress ❗
But you can calm yourself down by changing the way you breathe – control stress
Hypothalamus and pituitary gland
Pituitary gland
Hypothalamus
Location
Function
Location
Function
Sits above the pituitary gland
Put two sticks through both ears and one up the nose; where they meet is the pituitary gland location
Sits below the hypothalamus
Controls and regulates what the pituitary gland secretes
Anatomy
Secretes a number of hormones
Anterior pituitary (towards the front)
Posterior pituitary (towards the back)
Gland – epithelial and connective tissue
Neural tissue ⚠
Part of the brain, but sits in a region full of neural cell bodies
Sits in a cavity, a bony depression of the skull bone known as the sella turcica
Made up of cells ⚠
Linked to the hypothalamus via a stalk
The cell body (soma) is located in the hypothalamus
Pituitary tumour
Removed via trans-sphenoidal surgery via two methods
Sublabial approach
Endonasal approach
Goes through the upper lip to open a path between the hard palate in the roof of the mouth and the nose
Most common method of pituitary tumour removal
Goes through the back of the nostril using an endoscope to see and a curette to remove the tumour
Relatively painful
Minimally invasive
Stimulates the production of cortisol from the adrenal glands
Nervous system is NOT turned off in gut (there are still contractions)
Makes us want to go to the toilet
The cell body is connected to neuron axons that run down the stalk (infundibulum)
The axons leads to the axon terminals in the posterior pituitary where hormones are released into capillaries
Regulates blood calcium levels
Also synthesised by the follicular cells
Also known as thyrotropin
Enables sperm production
Ovaries
Also known as corticotropin
Endorphins
Pain receptors in the brain
Tropic or non-tropic?
Mammary glands