BIOL-182 Quiz #4 (Lectures #13-15)

What controls mammalian reproduction?

Hormones from the hypothalamus, anterior pituitary, and gonads

Where does endocrine control of reproduction begin?

@ the HYPOTHALAMUS, which secretes GnRH (gonadotrophin releasing hormone), which directs the anterior pituitary to secrete the gonadotropins FSH and LH (tropic hormones = towards; regulate the activity of endocrine cells/glands)

What do gonadotropins act on?

Both MALE and FEMALE gonads

What do FSH and LH support?

GAMETE FORMATION (gametogenesis) by stimulating sex hormone production by gonads --> adrenal glands also secrete sex hormones in small amounts

3 major types of steroid sex hormones produced and secreted by gonads

1. Androgens, mainly TESTOSTERONE (higher in males)

2. Estrogens, mainly ESTRADIOL (higher in females)

3. PROGESTERONE (higher in females)

In mammals, where does the function of sex hormones begin?

In the EMBRYO --> ex.) androgens produced in male embryos direct the appearance of primary sex characteristics of males

Primary sex characteristics

Structures directly involved in reproduction that are present at birth and comprise the external and internal genitalia --> penis and testes in MALES; vagina and ovaries in FEMALES

During sexual maturation, sex hormones in human males and females induce...

Formation of secondary sex characteristics

Secondary sex characteristics

Physical and behavioral differences between males and females that are not directly linked to the reproductive system --> often lead to SEXUAL DIMORPHISM (difference in appearance between the male and female adults of a species)

2 types of cells that FSH and LH act on in directing spermatogenesis IN THE TESTIS (in males)

1. FSH stimulates Sertoli cells

2. LH stimulates Leydig cells

Sertoli cells

- Stimulated by FSH

- Located within the seminiferous tubules

- Nourish developing sperm

- Focus on GAMETE MATURATION

Leydig cells

- Stimulated by LH

- Scattered in connective tissue between the tubules

- LH causes these cells to produce TESTOSTERONE and other androgens which promote spermatogenesis in the tubules

- Also secrete small quantities of many other hormones and local regulators (ex. oxytocin) to coordinate the activity of reproduction with growth, metabolism, homeostasis, and behavior

2 negative feedback loops that control sex hormone production IN MALES

1. TESTOSTERONE regulates the blood concentration of GnRH, FSH, and LH through INHIBITORY effects on the HYPOTHALAMUS and ANTERIOR PITUITARY

2. INHIBIN (a hormone that in males is produced by SERTOLI CELLS) acts on the anterior pituitary gland to REDUCE FSH SECRETION

Hormonal control of the testes

- Hypothalamus stimulates the release of follicle stimulating hormone (FSH) and luteinizing hormone (LH) from anterior pituitary --> caused by the release of GnRH from the HYPOTHALAMUS

- FSH stimulates sperm development

- LH stimulates interstitial cells to produce testosterone

- Levels of testosterone are fed back to hypothalamus and anterior pituitary to regulate sperm production (negative feedback)

Blocking GnRH receptors in the anterior pituitary would...

DECREASE TESTOSTERONE PRODUCTION --> if you block receptors, they cannot stimulate the release of gonadotropins, therefore inhibiting testosterone production --> ex.) blocking GnRH as a contraception method for nuisance deer

2 closely linked reproductive cycles in human females that are both controlled by cyclic patterns of endocrine signaling

1. Ovarian cycle

2. Uterine cycle

Ovarian cycle

- Defined by cyclic events in the OVARIES

- Once per cycle, a FOLLICLE MATURES and an oocyte is released

Uterine cycle

- Defined by changes in the UTERUS

- Called a MENSTRUAL CYCLE in humans and some other primates

What happens in each menstrual cycle?

The endometrium (lining of the uterus) THICKENS and develops a rich blood supply before being shed through the CERVIX and VAGINA if pregnancy does not occur

Impact of linking ovarian and uterine cycles

Hormone activity synchronizes ovulation with the establishment of a uterine lining that can support embryo implantation and development

Menstruation

Cyclic shedding of the blood-rich endometrium from the uterus that occurs in a flow through the CERVIX and VAGINA --> if an oocyte is not fertilized and pregnancy does not occur, the uterine lining is sloughed off, and another pair of ovarian and uterine cycles begins --> average = ~28 days, but can range from 20-40 days

Central role of the hypothalamus in human females

Regulating reproduction

When does the ovarian cycle begin?

When the hypothalamus releases GnRH, which stimulates the anterior pituitary to secrete small amounts of FSH and LH

FSH (follicle stimulating hormone)

Stimulates follicle growth, aided by LH, and the cells of the growing follicle start to make ESTRADIOL

Stages of the ovarian cycle

1. Follicular phase (days 0-14)

2. Ovulation (day 14)

3. Luteal phase (days 15-28)

Follicular phase of the ovarian cycle (days 0-14)

- Estradiol concentration slowly rises

- Follicles grow and oocytes mature --> several begin to grow with each cycle, but usually only one matures (the others disintegrate)

- The maturing follicle (containing a fluid-filled cavity) enlarges to form a bulge @ the surface of the ovary

What occurs when there is a LOW concentration of estradiol?

Inhibition of secretion of pituitary hormones, which in turn keeps the concentration of FSH and LH relatively LOW

What occurs when estradiol secretion by the follicle begins to rise steeply?

Levels of FSH and LH INCREASE SIGNIFICANTLY; Why? --> this high concentration stimulates gonadotropin secretion by causing the hypothalamus to increase output of GnRH --> a high estradiol concentration also INCREASES the GnRH SENSITIVITY of LH-releasing cells in the pituitary, further INCREASING the LH levels

When does the follicular phase end?

@ ovulation (day 14), about a day after the LH surge

Ovulation of the ovarian cycle (day 14)

In response to FSH and the peak in LH levels, the follicle and adjacent wall of the ovary rupture, releasing the secondary oocyte

Luteal phase of the ovarian cycle (days 15-28)

- A CORPUS LUTEUM is formed from the remnants of the follicle that has ovulated its oocyte

- Corpus luteum secretes PROGESTERONE and ESTROGEN, which exert negative feedback on the hypothalamus and pituitary

- Formation of the corpul luteum is triggered by the same LH surge that triggers ovulation --> however in the absence of LH (levels quickly decline after the surge) the corpus luteum begins to degenerate

Stages of the uterine (menstrual) cycle

1. Menstrual flow phase (days 1-5)

2. Proliferative phase (days 6-14)

3. Secretory phase (days 15-28)

If pregnancy does not occur, the low gonadotropin concentration @ the end of the luteal phase...

Causes the corpus luteum to DISINTEGRATE, triggering a sharp DECLINE in ESTRADIOL and PROGESTERONE concentrations --> this decline liberates the hypothalamus and pituitary from negative feedback loops --> the pituitary can then secrete enough FSH to stimulate the growth of new follicles, initiating the next cycle

Menstrual flow phase (days 1-5)

First stage of the uterine cycle when menstrual bleeding occurs

Proliferative phase (days 6-14)

Second stage of the uterine cycle when the endometrium regenerates and thickens

Secretory phase (days 15-28)

Third stage of the uterine cycle during which the rebuilt endometrium is enhanced with glycogen and lipid stores --> this phase is primarily under the control of PROGESTERONE and ESTROGEN (secreted from the corpus luteum during this time period)

Progesterone

Hormone produced by the ovaries which promotes the growth of the uterine lining --> "for gestation" = "for pregnancy"

What do birth controls block?

Ovulation --> contain the hormones PROGESTERONE and ESTRADIOL --> birth control pills prevent pregnancy by preventing production of GnRH, which results in NO SURGE of LH

What do hormonal responses to stress integrate?

Both the MIND and BODY

2 systems of coordination

1. Nervous system

2. Endocrine system

2 branches of the nervous system

1. Central nervous system

2. Peripheral nervous system

Central nervous system

Composed of the brain and spinal cord --> PROCESS information received through sensory systems and other parts of the body and activate appropriate reactions to the external/internal stimuli

Peripheral nervous system

Cell nerves are involved in sending sensory information to the BRAIN (sensory/afferent division) and also sending information from the brain to the rest of the body (motor/efferent division)

2 divisions of the peripheral nervous system

1. Somatic nervous system

2. Autonomic nervous system

Somatic nervous system

Controls muscles

Autonomic nervous system

Controls subconscious processes --> 2 divisions: SYMPATHETIC and PARASYMPATHETIC

Parasympathetic division

- "Rest and digest" --> calming systems that help return to long-term projects (i.e. reproduction and growth)

- Constricts pupils

- Stimulates salivation

- Constricts airways (brings back down the size of the tubes going into the lungs)

- Stimulates stomach, gall bladder, and intestine

- Contracts bladder

Sympathetic division

- "Fight or flee" --> arousal

- Dilates pupils

- Inhibits salivation

- Increases heart rate (circulation)

- Relaxes airways (respiratory)

- Inhibits stomach, gall bladder, and intestine

- Relaxes bladder

- Secretes EPINEPHRINE and NOREPINEPHRINE

How is the action of the sympathetic nervous system adaptive?

- Just a thought can activate the same system

- Nervous systems stimulate the ENDOCRINE SYSTEM (ADRENAL GLANDS in particular) --> *adrenal medulla* = epinephrine, *adrenal cortex* = cortisol

Short term stress response

The body's acute reaction to stress in which the sympathetic nervous system is stimulated --> also known as fight-or-flight response --> effects of the SYMPATHETIC NERVOUS SYSTEM

Short term stress response w/ the effects of epinephrine and norepinephrine

1. Glycogen broken down in glucose --> increases blood glucose

2. Increased blood pressure

3. Increased breathing rate

4. Increased metabolic rate

5. Change in blood flow patterns, leading to increased alertness and decreased digestive and kidney activity

What is the "pit in stomach" caused by?

Caused by blood flow leaving the stomach --> can be diverted to MUSCLES or BRAIN

How is epinephrine produced?

Produced specifically in the ADRENAL MEDULLA, where the amino acid tyrosine is transformed through a series of reactions to NOREPINEPHRINE

How can the same hormone (epinephrine) do so many different things?

Same receptors, but DIFFERENT INTRACELLULAR PROTEINS --> different receptors (could cause epinephrine to DILATE or CONSTRICT) --> opposite actions of the hormone by binding onto different subtypes of the receptor

What is the point of alpha (a) and beta (b) receptors to epinephrine?

- Binds both receptors to cause VASOCONSTRICTION and VASODILATION (actions within blood vessels)

- Allows epinephrine to target multiple multiple areas and therefore relay a larger variety of responses back --> opposite actions of the hormone by binding onto different subtypes of the receptor

How is cortisol produced?

Hypothalamus (CRH) --> anterior pituitary (ACTH stimulates cells of adrenal cortex to produce cortisol) --> adrenal gland (cortisol)

The release of cortisol from the adrenal cortex is stimulated by

ACTH --> during times of stress, the body can release cortisol after releasing its "fight or flight" hormones (ex. epinephrine) so it continue to stay on high alert --> also triggers the release of glucose from the liver for fast energy during times of stress, therefore INCREASING blood pressure

Function of cortisol

- Mobilizes internal fuel for quick use --> break down fats and proteins in muscles and liver

- Narrows capillary pores to prevent excess fluid loss from blood vessels --> can shut down pores in periods of high blood pressure

Animals with cortisol (and an adrenal gland) are able to constrict blood in the capillaries in order to...

Not lose blood when frightened (ex. with a stimulus like a siren) --> PORE FIGHTER

Adverse effects of long term elevation of cortisol

- Muscle wasting

- Reproductive inhibition

- Immunosuppression

2-pronged approach to stress (nervous and endocrine systems)

Involves both the nervous and endocrine system

- NERVOUS SYSTEM is activated, sends systems to the autonomic nervous system (SYMPATHETIC) --> epinephrine goes into the blood (acts like a protein, so it acts on cells very quickly) --> QUICKER PROCESS (seconds-minutes)

- ENDOCRINE SYSTEM: pituitary releases tropic hormone (ACTH), which goes to the ADRENAL GLAND to cause the release of CORTISOL (steroid hormone) --> slower process (~15 mins for increase in cortisol, hours later for response to cortisol)

What does cortisol cause a long-term increase in?

Breakdown of FATS and PROTEINS

What happens to capillaries and pores during phases where blood pressure is increased?

NARROWING of capillaries and pores occurs

Increased levels of cortisol cause a decrease in release of

ACTH --> negative feedback response

Time scale of response to stress

- SYMPATHETIC nervous system: rapid responses

- Epinephrine: seconds-minutes, causes an increase in blood glucose and redirects blood to tissues that help the body respond in a particular emergency

- Cortisol: hours/days/weeks --> acts to break down proteins for fuel, but can inhibit reproduction if elevation period is too long

Basic function of the nervous system

Collects information from the exterior

Basic unit of the nervous system

Neuron (nerve cell) --> nervous system has ~1 trillion

2 most important features of the nervous system

1. Highly interconnected

2. Electrically active

Neuron connections

- Signals travel down an AXON to the SYNAPSE, where it transmits signals to the other cells via NEUROTRANSMITTERS and potentially causes a change in it

- The "typical" neuron connects with 1000s of other neurons --> HIGHLY INTERCONNECTED

- ELECTRICALLY ACTIVE --> the inside of neurons has a NEGATIVE CHARGE --> reason for why they function so RAPIDLY

The inside of neurons has a ____ charge

NEGATIVE

Evolution of nervous systems

- Among the kingdoms of life, only ANIMALS have nervous systems

- Neurons generate electric signals pretty much the same way in all animals

- Neuron # and patterns of connections differ dramatically among animals --> due to differences in STRUCTURE --> STRUCTURE determines FUNCTION, which distinguishes behavior of one animal from another

All neurons are ____

FAST --> operate in MILLISECONDS

Facets of neural transmission

1. The battery

2. The trigger

3. The signal

4. The transmission

5. The connection

The battery: What sets the resting potential of a neuron?

- 2 kinds of ions: Na+ (sodium) and K+ (potassium)

- 2 kinds of movement: IN and OUT of the neuron

- 2 kinds of gradients: CHEMICAL (differences between concentrations INSIDE and OUTSIDE) and ELECTRICAL (differences in CHARGES --> + and -)

Sodium (Na+) gradients

Less concentrated inside the cell (CHEMICAL), but also POSITIVE SODIUM (Na+) is ATTRACTED to the NEGATIVE INSIDE of the neuron

Potassium (K+) gradients

Chemical gradient (STRONGER) wants to move OUTSIDE of the neuron b/c less concentration is there, but electrical gradient (WEAKER) wants it to move to the inside to the negatively-charge area b/c it is attracted electrically to it (potassium (K+) is positive)

You place a drug on the neuron that opens a lot of Na+ channels. What happens?

Na+ enters the neuron, and the neuron becomes more POSITIVE

How are the chemical an electrical gradients established? (battery)

- Permeability: K+ leaks out more than Na+ leaks in

- Pump: 2 K+ for every 3 Na+ out --> ASYMMETRIC

Opening Na+ channels

Membrane potential (mV) starts @ RESTING POTENTIAL, then reaches a THRESHOLD, which is eventually crossed to reach an ACTION POTENTIAL @ a particular point

Action potential

A neural impulse --> a brief electrical charge that travels down an axon

How is an action potential formed?

The coordinated opening and closing of ION CHANNELS --> takes 1 millisecond

4 steps of action potential formation

1. RESTING STATE: opens a few channels that get a little more positive

2. DEPOLARIZATION: sodium channel is opened

3. RISING PHASE OF THE ACTION POTENTIAL: sodium floods into the cells and gets POSITIVE very fast

4. FALLING PHASE OF THE ACTION POTENTIAL: sodium channels slam shut, but potassium channels now fly open --> potassium then leaves the cell --> ELECTRICAL gradient FLIPS, and now potassium wants to LEAVE the cell b/c of the concentration gradient and the electrical gradient (inside has become TOO POSITIVE)

What happens in the "downstroke" (phase 4) of the action potential?

K+ leaves the neuron, making it LESS POSTIVE

What drives K+ out of the neuron in the "downstroke (phase 4) of the action potential?

Chemical gradient and electrical gradient

Action potentials are ____ events

All-or-nothing --> DIGITAL (some events occur no matter how string or weak the stimulus is)

Intensity of stimulus depends on...

FREQUENCY of action potentials

The transmission: How do action potentials propagate?

- Action potentials are CONTAGIOUS --> move down the AXON

- When an action potential is formed, sodium enters the cell, making it more positive --> some positive ions leak out, causing another action potential to occur --> VERY RAPID, ~60 mph

Myelin sheath

Insulation that speeds up transmission --> neurons jumping from insulated to uninsulated regions (node to node) --> can move 3x as fast, ~200 mph

What kind of neurons does pain travel through?

Unmyelinated neurons

Components of the cell body

1. Cell body

2. Schwann cell

3. Node of Ranvier

4. Myelin Sheath

5. Axon

Schwann cell

Supporting cells of the peripheral nervous system responsible for the formation of the myelin sheath

Node of Ranvier

A gap between successive segments of the myelin sheath where the axon membrane is exposed

Highly connected cells via ____

SYNAPSES

Synapse

The space between 2 neurons

Big idea of neurons

Neurons are prepared through actions of pumps and leaks --> when it gets activated, ions flow in both directions --> forms ACTION POTENTIALS, which propagate down the neuron b/c they are CONTAGIOUS to the next (some positive ions leak out, causing another action potential to occur)

The trigger: What initiates an action potential?

Many inputs and sensations:

- Temporal and spatial summation

- The world via SENSE ORGANS --> crunching your entire would into one word: ACTION POTENTIALS

The connection: How do action potentials affect other neurons?

Synaptic transmission --> connections are called SYNAPSES in cells (usually 1000s of them) --> SENDING CELLS send action potentials to other other cells (RECEIVING CELLS)

Synapse gradients

From ELECTRICAL to CHEMICAL to ELECTRICAL

Neurotransmitters

Chemicals that transmit information from one neuron to another by crossing synaptic gaps between neurons

4 steps of action potential generation

1. An action potential arrives, depolarizing the presynaptic membrane

2. The depolarization opens voltage-gated channels, triggering an influx of Ca++ (calcium)

3. The elevated Ca++ concentration causes synaptic vesicles to fuse with the presynaptic membrane, releasing neurotransmitter into the synaptic cleft

4. The neurotransmitter binds t ligand-gated ion channels in the postsynaptic membrane --> in this example. binding triggers opening, allowing Na+ and K+ to diffuse through --> overall, making the cell more POSITIVE