Endocrine System - Bio 12

Endocrine system

Made up of endocrine glands

• Tissues that secrete hormones into circulatory system to be disseminated throughout body, regulates function of distant tissues + maintains homeostasis

Secretes hormones that coordinate slower but longer-acting responses to stimuli

Message travels through blood, reaches all tissues

Monitors/regulates using feedback loops

Endocrine vs Nervous system

Both carry out integration of body functions (communication/control)

Endocrine system - slow action + long duration, generalized areas + receptor sites

• Chemicals released into blood + carried through body

Nervous system - quick action + short duration, localized areas + effectors

• Conveys high-speed electrical signals along neurons (specialized cells)

• Autonomic nervous system does not require conscious control

• Parasympathetic - slows down

• Sympathetic - stimulates

Endocrine/nervous system communicate to regulate body functions

Brain, hypothalamus, pituitary monitor and control

Endocrine system includes these glands:

Brain:

Hypothalamus

• Controls endocrine system, maintains homeostasis, e.g. thirst, hunger, fatigue

Pituitary

• Things like growth, metabolism, reproduction

Pineal

• Melatonin, circadian rhythm

Lower neck:

Thyroid

• Metabolism, growth, development

Parathyroid

• Parathyroid hormone (PTH), maintains calcium levels in blood

Upper chest:

Thymus

• Makes white blood cells (T-cells)

Abdomen:

Adrenal

• Metabolism, blood pressure, immune system, stress

Kidney

• Filter blood, produce urine, red blood cell production

Pancreas (both endocrine and exocrine gland)

• Regulates blood sugar levels

Pelvis:
Ovary

• Produce hormones (e.g. estrogen), menstrual cycle

Uterus (muscle, not gland)

• Pregnancy, mammary gland (lactation)

Teste

• Produce hormones (e.g. testosterone)

Endocrine system does not include:

Exocrine glands, e.g. salivary glands, sweat glands, glands in the gastrointestinal tract

Exocrine tissues secrete products into ducts and then to outside of body, or to intestinal tracts

Control pathways and feedback loops

Common feature of control pathways is feedback loop connecting response to initial stimulus

Negative feedback regulates many hormonal pathways involved in homeostasis, is most common form of feedback

What is a hormone

An organic molecule (usually peptide or steroid, can also be amines) produced by tissue

Carried by bloodstream to another tissue(s) to affect physiological activity (e.g. growth, metabolism)

Can reach all parts of body, but only target cells are equipped to respond

• Some act on specific cells (e.g. gastrin on stomach cells)

• Some are non-target hormones (e.g. insulin acts on all cells b/c all cells have receptors for insulin)

Target cells - Cells that have a receptor for the hormones

Advantages of using chemical messengers

Chemical molecules can spread to all tissues through the blood

Chemical signals can persist longer than electrical ones

Many different kinds of chemicals can act as hormones

• Different hormones an target different tissues

Hormone classes

1. Steroids - made from cholesterol

2. Peptides - short amino acid chains

3. Amines - modified amino acids

Steroids

Lipids derived from cholesterol

Testosterone - male sex hormone, also needed by females, tissues convert estrogen to testosterone

Estradiol is responsible for many female sex characteristics, needed in males in small amounts, tissues convert testosterone into estrogen

• Similar to testosterone in structure

Steroid hormones are secreted by gonads, adrenal cortex (cortico steroids), placenta

Are hydrophobic

Peptides and amines

Most hormones are peptides

Examples: growth hormone (produced by pituitary gland), follicle-simulating hormone (FSH), which has carbohydrate group attached and is glycoprotein

Amines are derived from tyrosine and are secreted from thyroid and adrenal medulla