The Endocrine System

Endocrine System

A collection of glands that work together to maintain

The Theory of Communication

All communication has at least three parts
Sender –

Hormones

Hormones are chemicals released by glands that control the function/activity of

Body Communication

Sender?
Message?
Receiver?

Tissue that creates the hormone

The hormone itself

The target tissue

Autocrines vs. Paracrines

Autocrines – cells produce hormones that effect themselves

Paracrines –

How can chemicals alter cellular function?

Hormones can…

1. Alter cell membrane permeability
2. Stimulate synthesis of proteins or

Human Growth Hormone – Normal Amounts

Examples – HGH Abnormally High Amounts

Testosterone – Normal Amounts

Testosterone – Abnormal Amounts/ Gender Differences

Hormone Classification

3 Chemical classes
Amino acid based
Steroid-based (sterols)
Eicosanoid (lipid-based)
What is the most

Amino acid-Based Hormones

Water soluble, so can diffuse through blood and body

Receptor Proteins

Target cells have receptors for each hormone
Not every cell has

Water Soluble (Amino acid-based) Hormones

Fat-Soluble Hormones

Can go right through the cell membrane!
Bond with receptor proteins

Fat-Soluble Hormones

Hormone Life (Half-life)

Presence of a hormone in the blood is limited

Hormone Release

What controls the release/retention of hormones?
Humoral Stimulus – Blood levels

Regulation

Hypothalamus – regulates most hormonal release in the body
Monitors body homeostasis

Hypothalamus Hormones

The hypothalamus makes two hormones that are stored in the

Pituitary Gland

Bi-lobed structure that stores and produces hormone
Under the direct control

Pituitary Gland (Hypophysis)

Posterior Pituitary

Does not create, but rather stores hormones that are made

Anterior vs. Posterior Pituitary

Anterior Pituitary

Derived from epithelial tissue (secretory cells)
Creates MANY hormones de novo
Human

Pituitary Perfusion (Posterior)

Posterior Pituitary (PP) is perfused with one major artery

Pituitary Perfusion (Anterior)

Capillaries are “split” (form plexi) twice!
Primary capillary plexus
Secondary capillary

Thyroid Gland

Surrounds the trachea (bilateral lobes)
Produces the hormone thyroxin
Why is this

Thyroid Structure

Principal (Follicle) Cells – produce thyroglobulin
Colloid – stores thyroglobulin and

Thyroid Synthesis

Thyroglobulin made by follicular cells and goes into follicle
Iodine trapped

Thyroid Production

Calcitonin

Produced by the parafollicular cells in the thyroid
Release of calcitonin results

The Parathyroid Glands

Paired glands located on the posterior aspect of the

The Adrenal Glands

Divided into two sections
Adrenal Medulla (the core of the

Adrenal Cortex

Produces corticosteroids (derived from cholesterol!)
Each zone of the cortex produces

Adrenal Cortex – Zona glomerulosa

Produce mineralocorticoids
Regulate ion concentration in blood and

Glucocorticoids

Synthesized in zona fasciculata
Cortisol – steroid-based hormone
Release of cortisol promoted by

Gluconeogenesis

Where do sugars normally come from?
Gluconeogenesis -

Gonadocorticoids

Secreted in the zona fascicularis/reticularis
Most are weak androgens (precursors to testosterone

The Adrenal Medulla

Chromaffin cells produce catecholamines
Epinephrine
Norepinephine
Released during fight-or-flight stress
Increases heart

Pineal Gland

Located in the diencephalon
Produces melatonin, which causes drowsiness
Decreased light, received

Pancreas

Organ most directly related in regulating blood sugar
Two hormones produced
Glucagon –

Pancreas

Glucagon

When released from the pancreas,
causes the breakdown of glycogen (liver

Insulin

When released from the pancreas, insulin…
Enhances cellular uptake of blood glucose
Inhibits

Diabetes mellitus

Due to low or non-functional insulin
Since sugar cannot be absorbed

Diabetes Symptoms

In the kidneys, sugar lost in urine pulls water from

Ovaries

Ovaries – produce estrogen and progesterone
Estrogen – regulates monthly menstrual cycle
Progesterone

Menstrual Cycle