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