Human Physiology Basics

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Questions and Answers

What is the primary focus of physiology?

The study of chemical compounds in the body

The study of functions of living things (correct)

The study of evolutionary biology

The study of human anatomy

Which type of tissue is responsible for initiating and transmitting electrical impulses?

Connective tissue

Epithelial tissue

Muscle tissue

Nervous tissue (correct)

What does the term 'homeostasis' refer to in multiceullar organisms?

The differentiation of specialized cells

The process of cell division

The ability to maintain a stable internal environment (correct)

The evolutionary adaptation for survival

Which level of organization comes after the chemical level in the body?

Cellular Signup and view all the answers

What is a characteristic function of muscle tissue?

Facilitates movement Signup and view all the answers

How does negative feedback contribute to homeostasis?

By reversing changes to return to set points Signup and view all the answers

What is 'cephalization' in terms of organismal structure?

Concentration of nervous tissue at one end of an organism Signup and view all the answers

Which of the following statements regarding connective tissue is true?

It connects, supports, and anchors various body parts. Signup and view all the answers

What is the primary role of chemoreceptors in the sensory system?

Signal chemical binding to generate neural signals Signup and view all the answers

Which of the following receptor types is directly associated with the sensation of touch?

Mechanoreceptors Signup and view all the answers

How do action potentials convey information about the intensity of a stimulus?

By changing the frequency of action potentials Signup and view all the answers

What mechanism allows for the enhancement of edge and border detection in sensory neurons?

Lateral inhibition Signup and view all the answers

Which of the following senses relies on GPCRs for signal transduction?

Smell Signup and view all the answers

What is the effect of high frequency firing in sensory receptors?

It correlates with stronger touch sensation Signup and view all the answers

What type of sensory cells are primarily responsible for transmitting the sensation of sound?

Hair cells Signup and view all the answers

Which of the following correctly describes the role of photoreceptors?

They detect light and cause hyperpolarization Signup and view all the answers

What is a key aspect of the process of sensory transduction?

Converting physical stimuli into neural signals Signup and view all the answers

What is the basis of taste discrimination in the gustatory system?

Patterns of activity across different taste buds Signup and view all the answers

Which stimulus is detected by thermoreceptors?

Temperature variations Signup and view all the answers

What type of cells primarily process olfactory signals after chemoreceptors are activated?

Interneurons Signup and view all the answers

Which type of taste sensation does not involve GPCRs for its transduction?

Sour Signup and view all the answers

What is the primary function of osmoreceptors?

Regulate water balance by detecting osmotic pressure Signup and view all the answers

What is the primary function of negative feedback in homeostasis?

To return the controlled variable to its set point Signup and view all the answers

Which of the following statements best describes positive feedback?

It amplifies changes in the body’s conditions. Signup and view all the answers

What role does the Na+-K+ pump play in maintaining the neuron's resting potential?

It actively transports sodium out and potassium into the cell. Signup and view all the answers

What initiates an action potential in a neuron?

The depolarization at the axon hillock exceeds threshold potential Signup and view all the answers

What occurs during the repolarization phase of an action potential?

Na+ channels close and K+ channels open Signup and view all the answers

Which part of the neuron is primarily responsible for receiving signals?

Dendrites Signup and view all the answers

What is the physiological consequence of a homeostatic disruption?

It can result in illness or death. Signup and view all the answers

What is a key characteristic of interneurons?

They have more dendrites to process sensory information. Signup and view all the answers

How does a neurotransmitter trigger a signal in a postsynaptic neuron?

By binding to receptors on the postsynaptic membrane. Signup and view all the answers

What happens during the refractory period of a neuron?

The cell becomes hyperpolarized, preventing immediate firing of another action potential. Signup and view all the answers

What role do microvilli play in tissues like the intestines?

They increase surface area for nutrient absorption. Signup and view all the answers

During which phase do Na+ channels open and Na+ enters the neuron during an action potential?

Depolarization Signup and view all the answers

How is the membrane potential of a neuron primarily maintained at rest?

By the Na+-K+ pump actively transporting ions. Signup and view all the answers

What causes the positive spike in membrane potential during depolarization?

Open Na+ channels allowing sodium to enter. Signup and view all the answers

What mechanism sharpens an image by inhibiting surrounding neurons?

Lateral inhibition by horizontal cells Signup and view all the answers

How does the ear amplify sound before it reaches the inner ear?

Through the movement of the tympanic membrane and ossicles Signup and view all the answers

Which structure in the cochlea is primarily responsible for detecting high-frequency sounds?

The base Signup and view all the answers

What occurs during the phototransduction cascade initiated by light exposure?

Hyperpolarization of photoreceptor cells Signup and view all the answers

In the context of hair cell activation in the cochlea, what is the result of the downward motion of the basilar membrane?

Repolarization of hair cells Signup and view all the answers

Which type of cells are responsible for adjusting motion and brightness perception in the retina?

Amacrine cells Signup and view all the answers

What structural change occurs in the lens when focusing on distant objects?

The lens flattens to reduce light bending Signup and view all the answers

What initiates the release of neurotransmitters in hair cells during sound vibration exposure?

Bending of stereocilia against the tectorial membrane Signup and view all the answers

How do cones differ from rods in terms of their function in vision?

Cones have high acuity for color and are sensitive to light Signup and view all the answers

What is the role of bipolar cells in the visual processing pathway?

They clarify and sharpen signals from photoreceptors Signup and view all the answers

What is the primary function of the hypothalamus?

Links the nervous and endocrine systems Signup and view all the answers

Which part of the brain is primarily responsible for regulating consciousness and relaying sensory information?

Thalamus Signup and view all the answers

What type of muscle is characterized by its striated appearance and voluntary control?

Skeletal muscle Signup and view all the answers

What occurs during the power stroke phase of the cross-bridge cycle?

The myosin head pulls the actin filament towards the H Zone Signup and view all the answers

Which of the following is NOT a characteristic of long-term memory (LTM)?

Transient notifications from existing synapse function Signup and view all the answers

How are the A-band and I-band different during muscle contraction?

I-band contracts, A-band length remains unchanged Signup and view all the answers

What is the role of the limbic system in the brain?

Coordinates instincts, emotions, and motivations Signup and view all the answers

During what sleep stage does the majority of tissue growth and repair occur?

Stage 3 Signup and view all the answers

Which neurotransmitter is primarily involved in strengthening synaptic connections during learning?

Glutamate Signup and view all the answers

What is the basic contractile unit of a muscle called?

Sarcomere Signup and view all the answers

What type of movement is generated by smooth muscle?

Involuntary contractions Signup and view all the answers

How does the structure of the cerebral cortex relate to its function?

Grey matter contains neuronal soma for processing information Signup and view all the answers

What defines the role of basal nuclei in motor control?

Inhibits unwanted movements Signup and view all the answers

Which part of the brain is responsible for balance and coordination of movement?

Cerebellum Signup and view all the answers

What triggers the release of neurotransmitters at the axon terminal?

Opening of voltage-gated Ca2+ channels Signup and view all the answers

How does saltatory propagation enhance the speed of action potentials?

Through the insulation provided by myelin layers Signup and view all the answers

What occurs during the process known as temporal summation?

Repeated EPSPs occur in quick succession at a single synapse Signup and view all the answers

What is the primary function of glial cells in the nervous system?

Supporting and protecting neurons Signup and view all the answers

Which statement best describes the role of calmodulin in synaptic transmission?

Calmodulin activates protein kinase II (PK2) Signup and view all the answers

What best describes the consequence of Na+ channel inactivation during an action potential?

Repolarization of the axon segment Signup and view all the answers

What is the primary neurotransmitter involved in the contraction of skeletal muscles?

Acetylcholine Signup and view all the answers

Which of the following statements about chemical synapses is true?

They utilize neurotransmitters as chemical messengers Signup and view all the answers

What is the effect of dual innervation by the sympathetic and parasympathetic nervous systems?

They often have opposing effects on the same target organs Signup and view all the answers

What is the role of the inhibitory interneurons in reflex circuits?

To inhibit the contraction of opposing muscles Signup and view all the answers

What distinguishes photoreception from mechanoreception and chemoreception?

It requires specialized proteins that respond to light. Signup and view all the answers

What leads to the reabsorption of neurotransmitters after their inactivation?

Reuptake into the presynaptic terminal Signup and view all the answers

Which type of summation occurs when EPSPs are present simultaneously at multiple synapses?

Spatial summation Signup and view all the answers

What physiological reaction is triggered by the sympathetic nervous system during stress?

Dilation of bronchi Signup and view all the answers

What type of muscle is controlled by the somatic peripheral nervous system?

Skeletal muscle Signup and view all the answers

Which component initiates the contraction of skeletal muscle through the cross-bridge cycle?

Acetylcholine release from motor neurons Signup and view all the answers

What characterizes hydrophilic hormones in terms of their action on target cells?

They activate signal transduction pathways. Signup and view all the answers

Which of the following is a function of tropic hormones released by the anterior pituitary?

Stimulating other endocrine glands Signup and view all the answers

What is the primary role of insulin in blood sugar regulation?

It enhances glucose uptake by cells. Signup and view all the answers

How do hydrophobic hormones exert their effects on target cells?

By diffusing into the cell and binding to receptors. Signup and view all the answers

What defines direct hormones released from the anterior pituitary?

They act directly on non-endocrine tissues. Signup and view all the answers

Which feedback mechanism is involved when the pancreas releases glucagon due to low blood sugar levels?

Negative feedback Signup and view all the answers

What is the role of the T-tubules in muscle contraction?

To conduct depolarization into the muscle fiber Signup and view all the answers

In the endocrine system, how do neuroendocrine cells communicate?

By releasing hormones into the bloodstream Signup and view all the answers

Which characteristic is true of smooth muscle contraction?

It uses dense bodies for contraction. Signup and view all the answers

What hormone released from the pancreas acts to lower blood glucose levels?

Insulin Signup and view all the answers

Which statement accurately describes the function of the SA node in the heart?

It generates action potentials that spread through the atria. Signup and view all the answers

Which hormone is an example of a tropic hormone produced by the anterior pituitary?

Thyroid Stimulating Hormone (TSH) Signup and view all the answers

What occurs during diastole in the cardiac cycle?

Blood is flowing from the atria into the ventricles. Signup and view all the answers

Which action occurs due to sympathetic stimulation of the heart?

Increased norepinephrine excitement of cardiac fibers. Signup and view all the answers

What is the primary role of Purkinje fibers in the heart?

To transmit the action potentials through the ventricles. Signup and view all the answers

How does blood flow to skeletal muscles change during exercise?

It increases due to vasodilation in the muscle blood vessels. Signup and view all the answers

What is the effect of acetylcholine released via the vagus nerve on heart rate?

It slows the heart rate down and promotes vasodilation. Signup and view all the answers

What role do gap junctions play in cardiac muscle function?

They synchronize contractions by allowing action potentials to pass between cells. Signup and view all the answers

During which phase of the cardiac cycle do the ventricles actively pump blood into the arteries?

Systole Signup and view all the answers

What is the primary function of the descending limb of the Loop of Henle?

Passive reabsorption of water Signup and view all the answers

How does urea contribute to the renal medulla's osmotic gradient?

It is recycled to help concentrate the urine. Signup and view all the answers

Which hormone increases water reabsorption in the collecting ducts?

Antidiuretic hormone (ADH) Signup and view all the answers

What role do aquaporins play in the renal system?

They facilitate the passive diffusion of water. Signup and view all the answers

In the absence of ADH, what effect does this have on urine concentration?

Urine becomes more dilute. Signup and view all the answers

Which portion of the Loop of Henle is impermeable to water?

Ascending limb Signup and view all the answers

What triggers the upregulation of urea transport proteins?

Presence of antidiuretic hormone (ADH) Signup and view all the answers

Which characteristic describes aquaporin 2 (AQP2)?

It increases in number when ADH binds its receptor. Signup and view all the answers

What is the primary role of salivary amylase in the mouth?

Chemical digestion of carbohydrates Signup and view all the answers

Which type of teeth is primarily responsible for grinding food?

Molars Signup and view all the answers

How does the stomach maintain its acidic environment?

Through the action of parietal cells secreting HCl Signup and view all the answers

What role does gastrin play when food arrives in the stomach?

Stimulates the production of HCl and pepsinogen Signup and view all the answers

What is the primary function of the duodenum in the small intestine?

Chemical digestion and nutrient absorption Signup and view all the answers

Which enzyme is secreted by the pancreas to aid in protein digestion?

Trypsin Signup and view all the answers

What is the main reason the stomach's pH is kept low?

To activate digestive enzymes Signup and view all the answers

Which statement about bile is true?

It is secreted in response to fats in the duodenum Signup and view all the answers

Where does most nutrient absorption occur in the digestive tract?

In the small intestine Signup and view all the answers

What mechanism allows glucose to enter intestinal cells?

Na+-glucose cotransporter Signup and view all the answers

What is the function of pepsin in the stomach?

To break down proteins into amino acids Signup and view all the answers

What triggers the release of bicarbonate ions into the duodenum?

Stomach acids Signup and view all the answers

Which structure helps propel waste forward in the large intestine?

Muscular contractions Signup and view all the answers

What percentage of bile salts are reabsorbed in the terminal ileum?

95% Signup and view all the answers

What is the primary role of corticotropin releasing factor in the stress response?

Stimulates glucose production in the liver Signup and view all the answers

How does diffusion primarily occur in multicellular organisms?

Across short distances in respiratory surfaces Signup and view all the answers

What physiological change occurs when oxygen partial pressure is higher in the alveoli than in the capillaries?

Oxygen diffuses from alveoli to capillaries Signup and view all the answers

What advantage does hemoglobin provide in oxygen transport compared to myoglobin?

Hemoglobin carries oxygen in red blood cells efficiently Signup and view all the answers

Which factor causes a left shift in the oxygen dissociation curve of fetal hemoglobin compared to adult hemoglobin?

Greater affinity for oxygen in fetal hemoglobin Signup and view all the answers

How do veins differ from arteries in terms of blood pressure and volume?

Veins carry deoxygenated blood at high volume Signup and view all the answers

What mechanism prevents backflow in veins?

Valves within veins Signup and view all the answers

What is the primary determinant of fluid exchange in capillary beds?

The balance between blood pressure and osmotic pressure Signup and view all the answers

What is a critical function of pulmonary capillaries?

Facilitate the exchange of gases Signup and view all the answers

What occurs in the body due to increased cell activity and a decrease in pH?

Right shift of the hemoglobin dissociation curve Signup and view all the answers

Which component primarily facilitates the loading and unloading of oxygen in hemoglobin?

Cooperative binding Signup and view all the answers

What is the functional role of the trachea in the respiratory system?

Transport air to and from the lungs Signup and view all the answers

How does the structure of capillaries support their primary function?

High surface area and thin epithelial lining Signup and view all the answers

What significant effect does bulk flow have in the circulatory system?

Distributes oxygen rapidly throughout the body Signup and view all the answers

What happens to the majority of fluid that exits capillaries?

Returned through the lymphatic system Signup and view all the answers

What is the primary role of bile secreted by the liver?

Assists in fat digestion Signup and view all the answers

Which of the following is a function of pancreatic acinar cells?

Secretion of digestive enzymes Signup and view all the answers

What is the function of the gallbladder?

Stores bile Signup and view all the answers

What role do bacteria in the large intestine primarily serve?

Synthesize vitamin K Signup and view all the answers

What happens to bile salts in the terminal ileum?

They are reabsorbed into the bloodstream Signup and view all the answers

How do the kidneys help maintain acid-base balance?

By excreting hydrogen ions Signup and view all the answers

Which statement about the filtration process in the glomerulus is true?

Blood pressure drives the filtration process. Signup and view all the answers

Which substance is primarily reabsorbed in the proximal convoluted tubule?

Glucose Signup and view all the answers

What is the primary role of insulin in the body?

To facilitate the storage of glucose as glycogen Signup and view all the answers

What does the loop of Henle primarily aid in?

Water and sodium chloride retention Signup and view all the answers

Which type of waste is most toxic and excreted mainly by aquatic animals?

Ammonia Signup and view all the answers

What primarily occurs during the secretion stage in the nephron?

Addition of waste products to the filtrate Signup and view all the answers

Which process describes how water moves in osmosis?

Water moves from low to high solute concentration Signup and view all the answers

How do kidneys contribute to regulating blood pressure?

By producing renin Signup and view all the answers

Study Notes

Structure and Function: Homeostasis

Physiology is the study of the functions of living organisms, focusing on the mechanisms of body processes. Structure and function are inseparable.
Levels of organization include chemical (atoms/molecules), cellular (basic/specialized functions), tissues (4 types), organs (multiple tissues), body systems (groups of organs), and organism (interplay of systems).
Cephalization is the concentration of nervous system tissue at one end, a result of convergent evolution, relating to forward locomotion and predatory adaptations
Segmentation is the organization of the body into segments.
Homeostasis is the balance of cells in a multicellular organism. This balance is maintained by negative feedback mechanisms, where a change in a regulated variable triggers a response that opposes the initial change.
Positive feedback amplifies a change, not restoring homeostasis.
Homeostatic disruptions can lead to illness or death. Pathophysiology describes abnormal body function associated with disease.
Form and function are related: organ/tissue/system form often dictates its function. (e.g., alveoli's large surface area maximizes gas exchange; neuron organization optimizes signal transmission)

Nervous System I

The nervous system senses, responds to, coordinates movements, and regulates internal body functions.
Sensory neurons receive information at their dendrites and transmit information along their axons.
Interneurons have many dendrites to receive and integrate signals.
Action potentials (APs) are triggered at the axon hillock.
Synaptic stimuli are summed at the axon hillock and if sufficient to reach threshold trigger APs. APs travel down the axon, triggering neurotransmitter release.
Membrane potential is due to differences in ion concentrations across the neuron's membrane. Negative resting potential is maintained by Na+-K+ pumps and K+ leak channels.
Action potentials involve rapid changes in membrane potential due to opening/closing of voltage-gated Na+ and K+ channels.
The Na+/K+ ATPase maintains a negative resting potential and the rapid opening of Na+/K+ channels and subsequent opening and closing creates APs
Neurons transmit electrical signals which cause vesicle release when an AP reaches the axon terminal. These neurotransmitters bind with receptors on the postsynaptic cell that change the membrane potential.
Glial cells support neuron function; some insulate axons via myelin, increasing signal propagation speed.

Nervous System II

The nervous system (CNS and PNS) work together to sense, respond to environment, coordinate movement, and regulate internal body functions (somatic and autonomic).
Peripheral Nervous System: somatic (voluntary) and autonomic (involuntary). Autonomic NS subdivided further into sympathetic and parasympathetic.
The sympathetic and parasympathetic nervous systems often have antagonistic effects on visceral organs.
Reflex circuits make fast responses possible, underpinning animal's perception and response capabilities
Neurons receive both excitatory (EPSPs) and inhibitory (IPSPs) signals. Neurotransmitters at EPSP receptors cause depolarization (reducing membrane potential so further excitation is possible). Neurotransmitters at IPSP receptors cause hyperpolarization (increasing the membrane potential so excitation is less possible)
EPSPs bring the neuron to a threshold to trigger an AP; IPSPs don't reach the threshold
EPSPs (excitatory) cause depolarization and IPSPs (inhibitory) cause hyperpolarization.

Sensory Systems I

Sensory receptors detect stimuli (chemical, mechanical, light).
Sensory transduction converts stimuli into receptor potentials causing cell depolarization, and depending on the sensory receptor, there is a change in membrane potential and opening and closing of ion channels that subsequently cause signal transmission to the brain.
Chemoreceptors: smell and taste; Mechanoreceptors: hearing; Photoreceptors: vision.
Sensory receptors have differential sensitivities, varying excitation thresholds to a given stimulus. Information from receptors is conveyed (Afferent neurons) to the CNS.
Intensity, location, duration, and enhancement of edges/borders are conveyed by action potential firing rates and lateral inhibition, respectively.
Adaptation occurs to a continuous stimulus, leading to a reduced firing rate (e.g., not feeling clothes on skin after awhile.)
GPCRs (G-protein coupled receptors) are essential for certain sensory pathways, including smell and taste.

Sensory Systems II

Multiple sensory systems are processed and integrated in different areas of the brain (specific cortical areas for each sense).
Hair cells in the inner ear transduce mechanical stimuli (sound/movement) into neural signals.
The outer ear funnels sound waves to the eardrum; the middle ear amplifies vibrations; the inner ear contains the cochlea and vestibular system.
Sound frequencies stimulate different regions of the cochlea. Loudness depends on intensity.
Light activates retinal, changing opsin conformation which triggers a cascade that ends with hyperpolarization of photoreceptors.
The retina's layered structure (rods, cones, bipolar cells, ganglion cells) converts light into neural signals (via lateral inhibition that sharpens images and adjusts motion/brightness).

Sensory Systems III

The brain integrates information from multiple sensory systems in specific brain areas (cortex, thalamus, hypothalamus) to allow for a coordinated response.
The primary motor/somatosensory cortex in the frontal and parietal lobes are responsible for initiating and receiving sensory inputs/motor commands, respectively.
The Limbic system is important for learning, memory, emotions, spatial orientation, and motivations/rewards
Cognition encompasses the brain’s ability to process and integrate info, remember past events, solve problems, form ideas, etc.
Learning strengthens neural connections through synaptic changes.
Sleep facilitates learning and memory consolidation—particularly REM sleep and synaptic consolidation.
Consciousness involves awareness of surroundings, thoughts, and one’s existence.

Muscles

Muscles are organized from sarcomeres (actin & myosin filaments) to muscle fibers to bundles to the whole muscle.
Actin and myosin interact via the cross-bridge cycle to generate force and produce muscle contraction.
Smooth/striated (skeletal & cardiac) muscle types differ in structure and control via different branches of the NS; smooth is part of the autonomic, striated is somatic.
Muscle contraction starts when motor neurons stimulate muscle cells, resulting in Ca2+ release and sarcomere shortening through the cross-bridge cycle.

Endocrine Systems

The endocrine system functions with the nervous system. The endocrine system uses hormones for slow, widespread signaling, while the nervous system uses neurotransmitters for fast, targeted signaling.
Hormones are classified as hydrophilic (peptide/amine) or hydrophobic (steroid).
Hydrophilic hormones bind to cell surface receptors, activating second messenger pathways; hydrophobic hormones enter the cell to bind intracellular receptors, altering gene expression.
Tropic hormones from the anterior pituitary gland target other endocrine glands, whereas Direct hormones have direct effects on non-endocrine tissues.
Negative and positive feedback loops regulate hormone levels in the blood.
Feedback loops in the endocrine system maintain homeostasis by regulating various body functions including blood sugar regulation. Example of negative feedback loop: blood glucose homeostasis.

Respiration

Multicellular organisms use diffusion over short distances and bulk flow over long distances for gas exchange.
Alveoli (lungs) maximize surface area for gas exchange via diffusion between alveoli gases and capillaries.
Partial pressure differences drive gas diffusion.
Hemoglobin in red blood cells carries oxygen, facilitating loading/unloading.
Hemoglobin's oxygen dissociation curve illustrates oxygen loading/unloading and environmental shifts.

Circulation and the Heart

Vessels of different sizes (e.g., capillaries, aorta, vena cava) facilitate bulk flow and diffusion of blood components. Arteries and veins have structural differences (thickness, elasticity, valves) that reflect their differing functions in blood transport.
Blood pressure and osmotic pressure influence fluid exchange in capillaries (filtration, reabsorption).
The heart systematically pumps blood from the body to the lungs, then back to the body. The heart has chambers (atria/ventricles) with valves between them, which work together in coordinated contractions (systole/diastole) to move blood.
Specialized cardiac muscle cells create coordinated contractions via gap junctions.
The nervous and endocrine systems control heart rate based on body conditions. Stress responses lead to increased heart rate and blood flow via sympathetic signaling, while the parasympathetic nerve system leads to decreased heart rate & vasodilation

Ingestion, Digestion, & Absorption

The foregut (mouth to stomach) initiates mechanical and chemical digestion (teeth, tongue, saliva, amylase).
The stomach mixes food with gastric juices to break down food, primarily proteins. The stomach itself produces pepsin for protein breakdown, lipases for lipid degradation.
The midgut (small intestine) continues chemical digestion and absorption. Enzymes and bile salts from the pancreas and liver further break down fats, carbs, and proteins. Absorption via villi and microvilli. Glucose absorption involves Na+ co-transport.
The hindgut (large intestine) absorbs water and electrolytes.
Positive feedback loops regulate digestive processes in the duodenum.
The acidic environment of the stomach is crucial for protein digestion via pepsinogen/HCl activation.

Osmoregulation

Renal organs eliminate nitrogenous wastes and regulate water and electrolyte levels. Osmoregulation maintains the balance of water within cells.
Different nitrogenous waste products exist (toxicities vary)
Filtration occurs at the glomerulus.
The loop of Henle establishes a concentration gradient for water reabsorption (Descending limb; permeable to water. Ascending limb; permeable to salt).
Urea plays a role in this function.
Antidiuretic hormone (ADH) and aquaporin channels control water reabsorption in the collecting duct, regulating urine concentration.

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Test your knowledge of basic human physiology concepts in this quiz. Explore essential topics such as tissue types, homeostasis, and levels of organization. Perfect for students looking to strengthen their understanding of the human body.