Homeostasis

What is homeostasis?

Our body’s tendency to maintain internal conditions despite external conditions

What is negative feedback?

• process which stabilizes itself by reducing its output when the output’s effects are too great

• Examples :

  • Body temperature

  • Breathing

  • Water balance

  • Blood sugar

  • Thermoregulation

What are the 2 hormones that assist in regulating blood sugar + info on them, how they do it?

• Insulin

  • Made by beta cells

  • Lowers blood glucose levels

  • Helps cells take in glucose

• Glucagon

  • Made by alpha cells

  • Raises blood glucose levels

  • Stimulates liver to release stored glucose

Body’s response to heat and cold

Heat:

• Physiological : -sweating, dilation of blood vessels, thirsty

• Behavioural: -drink water, find shade

Cold:

• Physiological: -shivering, constriction of blood vessels

• Behavioural: -putting on gloves, seeking places with warmth, moving around to create heat

What is the purpose of the nervous system?

• Detects stimuli (changes inside and outside the body)

• Processes and interprets information

• Sends rapid signals to muscles and glands

• Coordinates responses to maintain homeostasis

Structure of Neuron

Compare electrically controlled and chemically controlled ion channels/gates in neurons

Electrically controlled channels/gates:

• Neurons have a resting membrane potential (~–70 mV) caused by unequal ion distribution (more K⁺ inside, more Na⁺ outside)

• Action potential starts when a stimulus makes the membrane voltage more positive (depolarization)

• If the voltage reaches the threshold (~–55 mV), voltage-gated Na⁺ channels open → Na⁺ rushes in → rapid depolarization

• Voltage-gated K⁺ channels open afterward → K⁺ flows out → repolarization (restoring negative inside)

Chemically controlled channels/gates:

• Found mainly on dendrites and cell body at synapses

• Open when a neurotransmitter binds to it

• ions (like Na⁺) flow in

• If enough ligand-gated channels open and the voltage reaches the threshold (~–55 mV) → triggers an action potential

• After the action potential starts, voltage-gated channels take over to accelerate it down the axon

Compare sensory, inter, and motor neurons

• Sensory neuron: brings info from body → brain/spinal cord

• Interneuron: processes info inside the CNS

• Motor neuron: sends info from brain/spinal cord → muscles/glands

How is action potential formed?

• Neuron at rest has a resting membrane potential (~–70 mV)

• Stimulus causes graded potential → small local change in voltage

• If voltage reaches threshold (~–55 mV) → voltage-gated Na⁺ channels open

• Na⁺ rushes in → depolarization (inside becomes more positive)

• Voltage-gated K⁺ channels open once hits +30mV → K⁺ flows out → repolarization

How does action potential move along the axon?

• Depolarization at one part of the axon triggers voltage-gated channels in the next section

• Action potential travels down the axon in a wave

• Myelin sheath speeds this up via saltatory conduction (jumps between Nodes of Ranvier)

How does action potential cross a chemical synapse?

• Action potential reaches axon terminal → voltage-gated Ca²⁺ channels open

• Ca²⁺ enters → triggers vesicles to release neurotransmitters into synaptic cleft

• Neurotransmitters bind to ligand-gated channels on postsynaptic neuron

• Postsynaptic membrane depolarizes → may trigger new action potential across next neuron

Autonomic Nervous System + Sympathetic vs Parasympathetic

Sympathetic:

• Prepares the body for “fight or flight” situations

• Increases heart rate, breathing, and blood flow to muscles

• Dilates pupils and airways

• Purpose: Get the body ready for stress, danger, or activity

Parasympathetic:

• Promotes “rest and digest” activities

• Slows heart rate and breathing

• Stimulates digestion and energy storage

• Purpose: Conserve energy and maintain normal body functions

Head lobes + Describe

• Frontal: voluntary movement, decision-making, personality

• Parietal: processes touch and spatial awareness

• Occipital: vision

• Temporal: hearing, memory, language comprehension

Brain Structure Functions

• Medulla oblongata: controls involuntary functions like heartbeat, breathing, and digestion

• Thalamus: relays sensory information to the appropriate part of the brain

• Cerebellum: coordinates balance, posture, and voluntary movement

• Corpus callosum: connects the two hemispheres of the brain and allows them to communicate

What is the purpose of the excretory system?

• removing metabolic waste products and other toxic substances from the body

• To maintain homeostasis, we must excrete to regulate our ionic balance and pH balance

• Regulates fluids and waste

Structures of the kidney

• Renal cortex: outer layer of the kidney; contains nephrons and filters blood

• Nephron: functional unit of the kidney; filters blood and forms urine

• Glomerulus: network of capillaries in the nephron; filters water, ions, and small molecules from blood

• Bowman’s capsule: cup-shaped structure surrounding glomerulus; collects the filtrate from blood

• Loop of Henle: part of nephron tubule; concentrates urine by reabsorbing water and salts

Three stages of urine formation

• Filtration

  • Occurs in the glomerulus

  • Blood pressure forces water, ions, and small molecules out of blood into Bowman’s capsule

  • Cells and large proteins stay in the blood

  • Forms filtrate (pre-urine)

• Reabsorption

  • Occurs in the proximal tubule, loop of Henle, and distal tubule

  • Useful substances (glucose, amino acids, water, ions) are reabsorbed back into the blood

  • Ensures the body keeps what it needs

• Secretion

  • Occurs in the distal tubule and collecting duct

  • Additional wastes, H⁺, and drugs are secreted from blood into tubule

  • Helps maintain pH and remove extra waste

Pituitary Gland

• Considered ‘master gland’

• Located within the cranium

• Two lobed gland within cranial cravity

• Produces hormones that control other endocrine gland

• Split into Anterior and Posterior lobe

• Portal vein connects pituitary gland to capillaries within hypothalamus

Anterior Pituitary Gland

• Makes up approx. 80% of pituitary gland

• Responsible for secreting several major hormones into the bloodstream (including those that then drive hormone secretion in other glands)

• For the 6 major hormones secreted by this gland, the hypothalamus signal the gland to secrete them

Posterior Pituitary Gland

• Responsible for storing and releasing two important hormones

• Located on the back of the Pituitary gland

• Contains ADH and Oxytocin, told by Hypothalamus when to store and release them through nerve signals

Pancreas Location and Function + Component

• Location: Located between small intestine and the spleen

• Function: Regulating blood sugar through production of hormones such as insulin and glucagon

Islets of Langerhans

Clusters of cells in the Pancreas which contain

• Alpha cells

  • Produce glucagon

• Beta cells

  • Produce insulin

How do Adrenal Glands help raise blood sugar levels?

• Adrenal cortex (outer part of adrenal glands) secrete hormone called glucocorticoids

• Glucocorticoids help raise blood sugar by:

  • Stimulating the production of glucose from non-carbohydrate sources.

  • Reducing how much glucose body cells take in, so more stays in the blood.

  • Promoting the breakdown of fats and proteins, releasing fatty acids and amino acids into the blood to be used as fuel when glucose is low.

Thyroid Structure + Function

butterfly-shaped endocrine gland in the neck that regulates metabolism, growth, and development by producing and releasing thyroid hormones (T3 and T4) and calcitonin

Parathyroid Structure + Function

The parathyroid glands are four small, oval-shaped endocrine glands located on the back of the thyroid gland that regulate blood calcium levels by producing parathyroid hormone (PTH).

Adrenal Glands Structure + Function

two small, triangular glands located on top of the kidneys that are crucial endocrine glands for regulating metabolism, stress response, blood pressure, and more

Testes Structure + Function

The testes are the male gonads, oval-shaped organs in the scrotum that function as both an endocrine and exocrine gland. As an endocrine gland, they produce and secrete hormones like testosterone

Ovaries Structure + Function

The ovaries are female endocrine glands with a structure of outer and inner layers, including the cortex (housing eggs and follicles) and medulla (containing blood vessels). Their function as endocrine glands is to produce hormones like estrogen and progesterone, which regulate the menstrual cycle, pregnancy, and fertility, as well as other hormones like inhibin and testosterone