animal physiology

Hormones

Chemical messengers that cause responses in target cells (lock-and-key)

Role of hormones

Help maintain stability and protect against drastic change

Animal hormones

Secreted into extracellular fluid to influence target cells

Endocrine hormones

Travel through blood and affect distant cells

Hormone specificity

Only affect cells with matching receptor proteins

Endocrine system

System made of hypothalamus, pituitary, and glands

Endocrine glands

Secrete hormones (adrenal and thyroid glands)

Lesser-known endocrine sources

Kidneys, intestines, fat cells, heart

Pituitary gland

Master gland controlled by the hypothalamus

Posterior pituitary

Neural tissue; secretes ADH and oxytocin from hypothalamus neurons

ADH

Targets kidneys; reduces urine output during dehydration

Oxytocin

Targets uterus and mammary glands; causes contractions and milk letdown

Anterior pituitary

Endocrine tissue; releases hormones when stimulated by hypothalamic hormones

Tropic hormones

Hormones that stimulate other endocrine glands

Growth hormone pathway

GHRH → GH → IGF-1 to stimulate bone and muscle growth

Thyroxine

Thyroid hormone that increases metabolic rate and requires iodine

Goiter

Enlargement of thyroid due to iodine deficiency

Parathyroid hormone

Raises blood calcium; targets bones and kidneys

Calcitonin

Lowers blood calcium (not active in humans)

Thyroxine regulation

TRH → TSH → thyroxine with negative feedback

Adrenal gland

Releases stress hormones

Epinephrine and norepinephrine

Trigger fight-or-flight responses

Cortisol

Steroid hormone that increases blood glucose and lowers inflammation

Insulin

From pancreas; lowers blood sugar by increasing storage in liver and fat cells

Asexual reproduction

Produces identical offspring quickly with one parent

Sexual reproduction

Involves two parents and increases genetic variation

Male reproductive system

Produces and delivers semen

Spermatogenesis

Continuous sperm production in seminiferous tubules

Epididymis

Stores and matures sperm

Vas deferens

Carries sperm to the urethra

Seminal vesicles

Produce most of semen volume

Bulbourethral glands

Produce a small portion of semen

Prostate gland

Produces ~30% of semen; alkaline

GnRH

Hypothalamus hormone that stimulates FSH and LH release

FSH (male)

Stimulates sperm production

LH (male)

Stimulates testosterone production

Testosterone

Stimulates sperm formation and secondary sexual traits

Female reproductive system

Receives and nourishes embryo

Oogenesis

Produces eggs before birth; eggs pause in meiosis

Uterine cycle

Thickening and shedding of endometrium

Ovarian cycle

Egg development and ovulation; controls uterine cycle

Follicle

Oocyte plus nurse cells

FSH (female)

Stimulates follicle development

LH (female)

Triggers ovulation

Corpus luteum

Produces estrogen and progesterone

Progesterone

Maintains uterine lining and inhibits FSH

Unfertilized egg

Corpus luteum degenerates; progesterone drops; menstruation begins

Fertilized egg

Progesterone remains high; menstruation stops

Neurons

Excitable cells that send and receive electrical signals; rarely divide

Glial cells

Support neurons; divide actively; do not send signals

Motor neurons

Control muscles and glands

Interneurons

Integrate and process information

Sensory neurons

Detect stimuli and convert them to electrical signals

Dendrites

Receive information from other neurons

Cell body

Processes information from dendrites

Axon

Carries electrical signals away from cell body

Synapse

Junction where neurons communicate with other neurons

Order of action potentials

dendrite, cell body, axon, synapse

Presynaptic neuron

Neuron that sends a signal

Postsynaptic neuron

Neuron that receives a signal

Synaptic cleft

Small gap between communicating neurons

Central nervous system

Brain and spinal cord

Peripheral nervous system

Sends information to and from the CNS

Somatic nervous system

Voluntary control of skeletal muscles

Autonomic nervous system

Involuntary control of glands and smooth/heart muscle

Sympathetic nervous system

Activates fight-or-flight responses

Parasympathetic nervous system

Promotes rest-and-digest functions

Forebrain

Includes cerebrum and hypothalamus; controls higher thought and homeostasis

Hypothalamus

Regulates homeostasis and endocrine function

Cerebrum

Controls thought, memory, and consciousness; divided into two hemispheres

Frontal lobe

Responsible for higher thought, personality, movement

Parietal lobe

Processes sensory information

Occipital lobe

Processes visual information

Temporal lobe

Processes sound, naming, pattern recognition

Midbrain

Relays sensory and motor information

Hindbrain

Controls breathing, heart rate, and automatic functions

Medulla

Controls vital involuntary functions

Cerebellum

Coordinates movement and muscle memory

Neurons as batteries

Neurons hold a charge due to ion differences inside and outside

Resting potential

-60 mV; inside negative, outside positive

Ion concentrations at rest

High Na+ outside; high K+ inside

Sodium-potassium pump

Uses ATP to maintain ion gradients (3 Na+ out, 2 K+ in)

Diffusion in neurons

Sodium and potassium move down concentration gradients through channels

Depolarization

Inside becomes less negative due to positive ions entering

Action potential

Rapid voltage spike caused by Na+ in, then K+ out

Threshold

Minimum voltage needed to trigger an action potential

All-or-nothing principle

Action potentials occur fully or not at all

Sodium channels

Open first during an action potential, causing depolarization

Potassium channels

Open second, causing repolarization as K+ leaves the cell

Repolarization

Return of membrane voltage to negative after AP peak

Sodium-potassium pump after AP

Restores original ion distributions using ATP

Wave propagation

Action potentials trigger the next section of axon to depolarize

AP movement

Sodium entry at one point triggers sodium channels farther down the axon

Chemical synapse

Communication using neurotransmitters across the synaptic cleft

Neurotransmitter release

Triggered when an action potential reaches axon terminal

Postsynaptic receptors

Channels that open when neurotransmitters bind

Effect of opening sodium channels

Makes postsynaptic neuron more likely to fire an action potential

Neurotransmitter cleanup

Enzymes break them down or they are reabsorbed

Signal integration

Cell body sums dendrite signals; if threshold is reached, AP fires

Action potential summary

Na+ entry raises voltage; K+ exit lowers voltage; APs are all-or-nothing