Unit 3: Homeostasis Part 1 - Nervous and Excretory System Flashcards
Define homeostasis.
the physiological state in which internal physical and chemical conditions are kept in a range that is suitable for biological processes
List the negative feedback mechanisms.
Stimulus, sensor (detects change), integrator (compares existing conditions with ideal conditions), effector (elements that act to return system to normal), response
Distinguish between negative and positive feedback.
Negative feedback - stimulus causes a response that compensates for the change (e.g. sweating when cold, thermostat)
Positive feedback - stimulus creates response that further increases change; does not result in homeostasis and causes conditions to be unstable (e.g. contractions during childbirth)
Define thermoregulation.
The regulation of internal temperature by negative feedback mechanisms
What is a neuron?
A nerve cell capable of conducting nerve impulses
What are dendrites?
Projections of cytosol that carry signals towards the nerve cell body
Besides neurons, what other cell makes up the nervous system and what is its function?
Glial cells; structure and support
List the 3 basic types of neurons.
sensory neurons (to the brain), interneurons, motor neurons (from the brain)
List the 3 major roles of kidneys.
- Remove waste
- Balance blood pH
- Maintain water balance
What 3 functions does urine formation depend on?
Filtration (of blood into the nephron), reabsorption (from nephron to body), secretion (from bloodstream into nephron)
Why does the Loop of Henle dip down into the medulla?
Since it has a high sodium content, when the descending loop of Henle (which is permeable to water but not salt) dips into the medulla, water is passively reabsorbed. In the ascending loop of Henle (which is permeable to salt but not water), sodium ions are reabsorbed back into the medulla (so the cycle can continue, and because now there is more water).
Describe what happens in the proximal tubule.
- Na+, glucose and amino acids are actively transported
- Cl- and HCO3- passively transported due to attraction
- water passively transported due to osmosis
- H+ may be secreted to balance blood pH
Describe what happens in the distal tubule.
- Na+ is actively transported if more water needs to be absorbed (it will follow through osmosis)
- H+ secreted to balance pH if necessary
Describe what happens in the collecting duct.
- Na+ is actively transported if more water needs to be absorbed
What is normal blood pH? Differentiate between acidosis and alkalosis.
Normal blood pH is 7.3 - 7.5.
Acidosis is when blood is too acidic; pH is too low.
Alkalosis is when blood is too basic; pH is too high.
Explain what happens when osmotic blood pressure is too high.
- osmoreceptors in hypothalamus detect high osmotic blood pressure, causing hypothalamus cells to shrink and nerve signals sent to pituitary gland
- pituitary glands release anti-diuretic hormones into the blood, increasing water absorption
- feelings of thirst occur; drinking lowers osmotic pressure of blood
- cells swell and stops ADH
Explain what happens when blood pressure is too low.
- the juxtaglomerular apparatus in the bowman’s capsule detects low blood pressure; specialized cells release renin
- renin converts angiotensinogen into angiotensin
- angiotensin causes construction of blood vessels and stimulates release of aldosterone from adrenal glands
- aldosterone is carried to kidneys and increases water and Na+ reabsorption (greater blood volume = higher pressure)
Are osmotic blood pressure and typical blood pressure examples of negative or positive feedback?
Negative
What is deamination?
When amino groups are removed from amino acids when proteins are broken down; the amino groups are then converted into ammonia and the rest of the amino acid is used for energy
What are the 2 nervous systems and how are they different?
Central nervous system: brain and spinal cords; Peripheral nervous system: all other nerves, carrying info to and from CNS
What are the 2 types of nerves in the peripheral nervous system and how are they different?
Somatic nerves (voluntary movements), Autonomic nerves (involuntary; organs like stomach, heart)
What are the 2 types of somatic nerves and how are they different?
Sensory nerves (pick up & transport info. about environment; to the brain), Motor nerves (stimulate response; from the brain)
What are the 2 types of autonomic nerves and how are they different?
Sympathetic (prepare body for stress); Parasympathetic (return body to normal after stress)
What is a reflex arc?
A neural circuit that travels through the spinal cord but does not require coordination of the brain; resulting in an immediate “reflex” response
Describe what a resting nerve cell looks like.
More Na+ on the outside of the membrane than K+ on the inside, resulting on a net positive on outside and net negative on inside; polarized
What is a synapse?
The site at which neurons connect
Describe what a stimulated nerve cell/action potential looks like.
Stimulus causes Na+ in the membrane to open, causing charge reversal; Na+ rush in and are attracted to negative charge further along the axon; disturbance causes more gates to open; depolarized
Describe what a refractory nerve cell looks like (back to resting).
Na+ / K+ pumps restore original charge; repolarized
What’s the difference between a pre-synaptic cell and a post-synaptic cell?
Pre-synaptic: neuron that transmits signal
Post-synaptic: neuron that receives signal
Sympathetic nerves have ___ preganglionic nerves and ___ postganglionic nerves. Parasympathetic nerves have ___.
Sympathetic nerves have short preganglionic nerves and long postganglionic nerves. (Parasympathetic have opposite)
Difference between chemical synapse and electrical synapse
In chemical synapse, neurotransmitters diffuse across synaptic cleft, binding to receptors in the plasma membrane of the post-synaptic nerve. In electrical synapse, pre- and post-synaptic nerves make direct contact and electric current is passed through a gap junction.
What is acetylcholine and how does it work?
Acetylcholine is a neurotransmitter that once stimulated, must bee destroyed in order to allow the post-synaptic nerve to return to resting; the enzyme that destroys it is called cholinesterase
What is a threshold level?
The minimum stimulus required to produce action potential in a nerve cell
How does the brain distinguish between small and large stimuli?
impulse of greater frequency and more nerve cells stimulated
What is alzheimer’s disease?
memory loss that affects daily function
Which stage of the nerve cell has the most active pumps and why?
Refractory; Na+ and K+ must be pumped to return to resting position
What is hyperpolarization?
When there is an even larger potential difference across the membrane, ensuring that the nerve cell DOES NOT carry the impulse (e.g. when you need one muscle to relax so the other can contract)
What are catabolic reactions?
When waste materials are produced as the body breaks down complex molecules
The ascending loop of Henle is permeable to ___, while the descending loop of Henle is permeable to ___.
ascending - permeable to salt
descending - permeable to water
Hemodialysis vs. peritoneal dialysis
Hemodialysis: dialysis machine connected to vein, solute levels balance, waste removed
Peritoneal dialysis: dialysis fluid pumped into abdominal cavity; cavity membrane filters waste from blood (can be done at home)
What is an example of positive feedback in the human body?
Childbirth; uterine contractions stimulate release of oxytocin, which further increases contractions
What happens after neurotransmitter molecules
diffuse across the cleft and bind to receptors in the plasma membrane of the postsynaptic cell?
channels open allowing ions to flow, generating an impulse in the nerve cell
What are the gaps between myelin sheaths called?
Nodes of Ranvier
What is multiple sclerosis? (M.S.)
Myelin is attacked by the immune system, blocking/slowing the transmission, causing weak muscles, numbness, coordination issues
Which feature of neurons ensures the one-way movement of action potentials?
The refractory period
