SBI4U chapters 8&9 - NS and endocrine system

Homeostasis

Tendency for body to maintain a constant internal environment

What disturbs homeostasis

External and internal stimuli

Components of a feedback system

Sensor (affector), control centre, effector

Sensor/affector

Detects changes in condition and sends message to control centre

Control centre

Acts as a regulator, receives info from sensors, determines appropriate response and sends signals to effectors

Effector

Responds to signal from control centre and changes environment to restore balance

Negative feedback loop

Homeostasis is returned to normal

Positive feedback loop

Strengthens change in variable (ex. contractions)

Nervous system

Senses and responds to change within body and external environment and regulates body structures/processes to maintain homeostasis

Central nervous system

Brain and spinal cord - processes info sent by nerves

Peripheral nervous system

Nerves that carry sensory messages to CNS and sends messages from the CNS to muscles and glands

Neurons

Structural units of the nervous system

Glial cells

Nourish neurons, remove waste from them, and prevent infection (ex. schwann cells)

Types of neurons

Sensory neurons, interneurons, motor neurons

Sensory neuron

Transmit impulses from the sensory receptors to the CNS

Interneuron

Act as a link between sensory and motor neurons

Motor neuron

Transmits information from the CNS to effectors

Membrane potential

Charge separation across membrane of a neuron (-70mV)

Na+/K+ pump

Uses ATP to transport 3 Na+ out of the cell and 2 K+ into the cell

Action potential

Change in the electrical membrane potential of a neuron that allows it to transmit signals

Synapse

Space between 2 neurons

Structure A

Cerebellum - involved in posture, reflexes, motor skills

Structure B

Medulla oblongata - Coordinates bodily functions for homeostasis like HR

Structure C

Pons - Relay centre between neurons of right/left halves of the cerebrum

Structure D

Midbrain - Processes info from neurons in eyes, ears, and nose

Structure E

Thalamus - connects various parts of the brain together

Structure F

Hypothalamus - regulates BP, HR, temp, emotions, controls pituitary gland

Structure G

Cerebrum - largest part of the brain, memory, consciousness, language

Hormone

Chemical messenger

Endocrine gland function

Secretes hormones into the bloodstream

Glands/organs of endocrine system

Pituitary, pineal, thyroid, parathyroid, adrenal glands, hypothalamus, thymus, pancreas, testes, ovaries

Target cells

Contains receptor cells for hormones

Water soluble hormones

Hormone binds to receptor, activates ATP→ cAMP

Lipid soluble hormones

Hormone diffuses through membrane, binds to receptor inside nucleus, activates mRNA synthesis → protein synthesis

Pituitary gland lobes

Posterior and anterior

Posterior pituitary gland

Stores and secretes ADH and Oxytocin (produced in the hypothalamus)

Anterior pituitary gland

Produces and secretes FSH, LH, TSH, ACTH, PRL, hGH

Pathway of hGH

Pituitary gland → hGH production → Liver → growth factors from liver → bone, muscle, fat cells

Hypersecretion of hGH

Gigantism (childhood) acromegaly (adulthood)

Hyposecretion of hGH

Dwarfism

Thyroid gland

Regulates metabolism, secretes thyroxine (T4)

Thyroxine

Targets cells in the heart, skeletal muscles, liver, kidneys

Low production of T4

Hypothyroidism or cretinism

Overproduction of T4

Hyperthyroidism, Grave’s disease

Pathway of thyroid feedback loop

Hypothalamus → TRH → pituitary gland → TSH → thyroid gland → T4 Production → inhibits release of TSH and TRH

Calcium homeostasis

Calcium levels are regulated by calcitonin and PTH

Adrenal glands

Regulates stress response and blood sugar

Components of adrenal glands

• Adrenal medulla

• Adrenal cortex

Adrenal medulla

Secretes epinephrine and norepinephrine - regulates short term stress

Adrenal cortex

Produce glucocorticoids and mineralocorticoids - trigger long term stress

Most abundant glucocorticoid

Cortisol - ACTH targets adrenal cortex, which secretes cortisol

Hormones of the pancreas

Insulin and Glucagon

Islets of langerhans

Clusters of endocrine cells that secrete hormones of the pancreas

Insulin

Secreted by beta endocrine cells, lowers blood glucose

Glucagon

Secreted by alpha endocrine cells, increases blood glucose

Functions of the endocrine system

• metabolism

• Growth and development

• sexual function

• sleep

• mood

• stress

• response to injury

Gonads

Pair of organs that produce reproductive cells and sex hormones

Sex hormones

Controls the development and function of the reproductive system and secondary sex characteristics

Seminiferous tubules

Where sperm are produced

Pathway of sperm

Made in seminiferous tubules → Transported to epididymis → Matured sperm go to ductus deferens to be stored

Semen

Sperm mixed with fluids from seminal vesicles, cowper’s gland, and the prostate gland

Puberty pathway (male)

Hypothalamus produces GnRH → acts on ant. pit. gland → releases FSH and LH → testes produce sperm and release testosterone

Male hormone regulation

FSH causes the seminiferous tubules to release inhibin

Inhibin

Produced by seminiferous tubules to inhibit the production of FSH to regulate male hormones

Endometrium

Uterine lining

Pathway of an egg

Stored in ovaries → once fertilized, moves to oviduct → goes to uterus

Estrogen

Female sex hormone produces in ovaries - maintains sexual organs and secondary sex characteristics

Progesterone

Female sex hormone produced by corpus luteum to prep the uterus for a fertilized egg

Ovarian cycle pathway

increase in FSH → follicle matures → follicle releases estrogen and progesterone → ant. pit. inhibits FSH → estrogen triggers GnRH release → LH also released → follicle bursts and ovum is released