BILD 2 Midterm 4

How is pressure involved in the movement of water & nutrients in plant xylem & phloem?

• Xylem

  • Water moves from roots → leaves

  • No pumps in the roots

  • Transpiration at the leaves lowers pressure, so water evaporates through stomata

  • Very low pressure in the leaves causes water to be pulled upward from higher pressure in the roots

  • Movement occurs because of a pressure gradient created by evaporation at the top

• Phloem

  • Sugar is actively loaded into phloem at source cells in the leaves

  • High sugar concentration draws in water by osmosis, increasing pressure

  • At sink tissues (roots/storage), sugar is unloaded

  • Water leaves, lowering pressure

  • Sugar moves from high pressure (source) to low pressure (sink)

How is pressure involved in the movement of blood in vertebrates?

• The heart acts as a pump

• During ventricular systole, contraction increases pressure in arteries

• Blood flows from high pressure (ventricles/arteries) to lower pressure (capillaries → veins → atria)

• Pressure gradually decreases along pathway: Arteries → Arterioles → Capillaries → Venules → Veins

• Ventricles generate the most pressure because they have thicker muscle walls

How does blood flow through the four chambers of the heart, the great vessels, lungs, and the blood vessels?

• Blood passes the heart twice

• Body to heart (Systemic circuit) (deoxygenated)

  • Body capillaries → Venules → Veins → Vena cava → Right atrium

• In heart to lungs (Pulmonary circuit)

  • Right atrium → Right ventricle → Pulmonary artery → Lung capillaries → Pulmonary veins → Left atrium → Left ventricle

• Heart to body (System circuit) (oxygenated)

  • Left ventricle → Aorta → Arteries → Arterioles → Capillaries

• Arteries → Arterioles (Away from heart)

• Veins → Venules (Toward heart)

Draw out the ECG associated with heart beat and describe what is occuring during each section of the graph.

• P wave

  • Atrial contraction

  • Generated by the SA node

  • Atrial depolarization occurs

• QRS

  • Ventricular contraction

• T wave

  • Ventricular relaxation

What are the components of the circulatory system?

• Fluid in which materials are transported (blood)

• A pump to move the fluid around (heart)

• Vessels to provide controlled paths (veins, arteries, capillaries)

What are the roles of the veins, venules, capillaries, arterioles, & arteries?

• Veins: Carry blood toward the heart

• Venules: Connect capillaries to veins

• Capillaries: Allow for exchange of O₂/CO₂, nutrients, & waste

• Arterioles: Control blood flow into capillaries & help regulate blood pressure

• Arteries: Carry blood away from the heart

What is the cardiac cycle, & what it its order?

• Cardiac cycle: One complete phase of pumping & filling

  • Contraction phase is systole

  • Relaxation phase is diastole

• Order:

  • Atrial & ventricular diastole

    • Atria & ventricles are relaxed, & blood is returning to the heart

  • Atrial systole (ventricular diastole)

    • Atria contract, ventricles are still relaxed

  • Ventricular systole (atrial diastole)

    • Ventricles contract

    • Pushes blood to the next structure

What happens if the SA node is destroyed?

The AV node becomes the pacemaker, and there are no P waves

What happens if the atria do not depolarize normally?

• Atrial contraction is abnormal or absent

• Ventricles still contract, but rhythm may be slower

How does the electrical signal travel in the heart?

0. Sinoatrial node: Pacemaker

1. Spreads to atria

2. Spreads to atrioventricular node

3. Spreads down the septum

4. Spreads out to both ventricles

What are the differences between systolic & diastolic blood pressure?

• Systolic blood pressure

  • Arterial blood pressure during ventricular contraction

  • It is the higher number in a blood pressure reading because ventricular contraction generates the greatest pressure

  • Pumping pressure

• Diastolic pressure

  • Arterial blood pressure during ventricular relaxation

  • It is the lower number because the heart is not actively contracting, so arterial pressure falls

  • Resting pressure

What are cross-sectional & total cross-sectional area, & what is the pattern in the body?

• Cross-sectional area: The area of a vessel if you slice it & look at the opening

• Total cross-sectional area: The sum of all vessels at that level

• Pattern in the body:

  • Small in aorta (one large vessel)

  • Larger in arteries

  • Largest in capillaries (because there are millions of them)

  • Decreases again in veins

• Capillaries have the greatest total cross-sectional area

How is velocity related to total cross-sectional area? What is the pattern of blood velocity & why?

• Total cross sectional area & velocity are inversely related

• If total cross-sectional area increases → velocity decreases

• If total cross-sectional area decreases → velocity increases

• Pattern:

  • Highest near heart (aorta, arteries)

  • Decreases dramatically in capillaries

  • Increases somewhat again in veins (but not as high as arteries)

• Cause:

  • Pressure (higher pressure → faster velocity)

  • Total cross-sectional area (lower area → Faster velocity)

How is pressure related to total cross-sectional area? What is the pattern of blood pressure?

• Pattern:

  • Highest in aorta & arteries

  • Gradually decreases through arterioles

  • Much lower in capillaries

  • Lowest in veins & vena cavae

• Cause:

  • Pressure is generated by ventricular contraction

  • As blood moves through vessels, energy is lost due to:

    • Stretching of vessel walls

    • Friction within vessels

• Pressure steadily declines with distance from heart

What are pressure, total area, & velocity like in the aorta, capillaries, & veins?

• Aorta

  • High pressure

  • Low total area

  • High velocity

• Capillaries

  • Lower pressure

  • Highest total area

  • Lowest velocity

• Veins

  • Very low pressure

  • Lower area than capillaries

  • Moderate velocity

How is blood pressure controlled homeostatically?

• If blood pressure is low, heart rate increases & arteries & arterioles constrict, making blood pressure rise

• If blood pressure is high, heart rate decreases & arteries & arterioles relax, making blood pressure fall

How do changes in body posture affect homeostatic control of blood pressure?

• When a person stands up suddenly:

  • Gravity pulls blood downward

  • Less blood returns to the heart

  • Arterial blood pressure falls

• Homeostatic response:

  • Baroreceptors detect less stretch

  • Signal sent to medulla

• Effectors respond:

  • Heart rate increases

  • Arteries & arterioles contrict

• Result:

  • Blood pressure rises back toward the set point

  • If this reflex did not occur → Dizziness or fainting

How do changes in baroreceptor function affect homeostatic control of blood pressure?

• Typically, when blood pressure increases:

  • Baroreceptors detect increased stretch

  • Medulla decreases heart rate

  • Arteries relax (vasodilation)

  • Blood pressure falls toward normal

• If baroreceptors cannot detect stretch:

  • Changes in blood pressure are not sensed properly

  • The medulla does not adjust heart rate or vessel diameter appropriately

  • Blood pressure becomes unstable

  • Standing up could cause prolonged drops in pressure

• If baroreceptors reset to a higher set point, like in chronic hypertension:

  • High blood pressure is treated as acceptable

  • Homeostatic correction does not occur

  • Hypertension (high blood pressure) persists

How will blood pH levels change when the kidney reabsorbs bicarbonate ions? When bicarbonate ions are secreted?

• Reabsorption

  • From filtrate back to blood

  • Adds bicarbonate back to the blood

  • Blood pH increases (becomes more basic)

  • Occurs when body needs to correct low blood pH

• Secretion

  • From blood to filtrate

  • Removes bicarbonate from the blood

  • Blood pH decreases (becomes more acidic)

  • Occurs when body needs to correct high blood pH

Map out how blood pH is homeostatically controlled.

Map out the creation, processing, & path of filtrate in the human kidney.

1. Glomerulus: Blood pressure forces arteriole blood through slits to make the filtrate. Small things like water, ions, & sugars can go through the filter, but not cells or proteins.

2. Proximal tubule

• Filtrate has been made, so things can go back into the blood

• Glucose, amino acids, water, sodium, & bicarbonate are reabsorbed by blood

• Most of the reabsorption is done here

• The filtrate ends isosmotic

3. Descending nephron loop

• Water leaves filtrate & is reabsorbed into the blood

• Filtrate ends hyperosmotic

4. Ascending nephron loop

• Sodium is reabsorbed into the blood

• Extracellular fluid in medulla is salty

• Actively pumps salt out

• Filtrate ends hyposmotic

5. Distal tubule

• Water is reabsorbed if there is ADH, and sometimes bicarbonate is reabsorbed

• Filtrate ends hyposmotic without ADH, isosmotic with ADH

6. Collecting duct

• Water is reabsorbed if there is ADH because the ADH inserts aquaporins into the membrane, which allow water to flow out because the medulla fluid is saltier

• Sometimes sodium & bicarbonate are reabsorbed into the blood

• Bicarbonate is sometimes secreted into the filtrate

• Filtrate ends hyposmotic without ADH or hyperosmotic with ADH

What happens when glomerular filtrate rate is low? High?

• Low GFR

  • Waste products stay in tubule too long & move back into the body

  • Too much fluid is retained in blood

  • Filtration stops & wastes/excess fluids remain in blood

• High GFR

  • Important materials flushed out with urine before they’re recovered

  • Too much fluid loss

  • Damage to glomerular capsule & kidney failure

How do the kidneys control GFR?

• Myogenic mechanism

  • Smooth muscle around the arteriole detects stretch & controls the arteriole’s size

  • High blood pressure stretches the arteriole → arteriole constricts → less blood in kidney → GFR lower

  • Low blood pressure → arteriole is not stretched → more blood in kidney → GFR higher

  • Local; only affects the glomeruli

  • Controls how much blood reaches the glomeruli

  • More blood flow → higher GFR

• Controlling the renin-angiotensin-aldosterone system

  • Global; affects the whole body

  • Controls the blood pressure of all the body’s blood

  • Higher blood pressure → higher GFR

How do changes in the renin-angiotensin-aldosterone system affect blood volume & pressure?

• Low GFR causes the release of the hormone renin

• Renin causes the formation of angiotensin I

• Angiotensin I turns into hormone angiotensin II

• Angiotensin II causes the adrenal glands to release the hormone aldosterone

• Aldosterone increases the reabsorption of sodium in the distal tubule & collecting duct, making the blood saltier

• Blood pressure & volume increase because the increased salt concentration in the blood attracts more water through osmosis

What are the different types of osmolarity?

• Hyperosmotic → Concentrated

• Isosmotic

• Hyposmotic → Dilute

How do the functions of the distal tubule & collecting duct change with & without ADH?

• With ADH: Water is reabsorbed from the filtrate into the urine

  • In the distal tubule, filtrate stays hypotonic & ends isotonic

  • Fluid around the collecting duct is very salty, so filtrate goes from isotonic to hypertonic

• Without ADH: Water is not reabsorbed & stays in the filtrate

  • In the distal tubule, filtrate starts & ends hypotonic

  • In collecting duct, filtrate starts & ends hypotonic

How is blood osmolarity homeostatically controlled? Map it out.

When osmolarity is high:

• Hypothalamus contacts other parts of the brain, to create a feeling of thirst

• Hypothalamus tells the posterior pituitary to release more of the hormone anti-diuretic hormone (ADH)

When osmolarity is low:

• Hypothalamus tells the posterior pituitary to release less of anti-diuretic hormone (ADH)

Map out the effects of angiotensin II.

Map out the flow of information in the nervous system.

What are the different types of muscle? What are sarcomeres & do they have sarcomeres?

• Skeletal

  • Attached to bones

  • Voluntary movement

  • Have sarcomeres

• Cardiac

  • Walls of the heart

  • Involuntary movement

  • Have sarcomeres

• Smooth

  • Walls of hollow, visceral organs

  • Involuntary movement

How do thin filaments, thick filaments, and Z lines move during muscle contraction?

• During contraction, thick & thin filaments slide together lengthwise

• Thin filaments (actin) slide toward the center of the sarcomere

• Thick filaments (myosin) stay in the same position

• Z lines move closer together as the sarcomere shortens

What are the steps of skeletal muscle fiber contraction?

1. Neuron has an action potential, which activates the neuromuscular junction

• In the neuromuscular junction:

  • The action potential in the neuron opens voltage-gated calcium channels

  • Calcium influx into the neuron causes the release of acetylcholine

  • Acetylcholine binds to its receptor on the muscle fiber, opening a channel that lets in sodium

  • Acetylcholine is broken down in the cleft by acetylcholinesterase

2. The muscle has an action potential, and the signal propagates to the rest of the muscle

3. Muscle contracts using cross bridge cycling

How is muscle contraction influenced by calcium?

• Without calcium

  • Myosin heads cannot bind to actin because tropomyosin is bound to actin and is in the way

• With calcium

  • Ca²⁺ binds to troponin

  • Troponin moves tropomyosin off the actin binding sites so the actin & myosin can form cross bridges

  • Myosin head turns & pulls thin filaments to contract

  • ATP binding to the myosin detaches the cross bridges

  • Energy from ATP hydrolysis moves myosin back into the initial state

What are the differences between the sympathetic & parasympathetic nervous system?

• Parasympathetic

  • Rest & digest

  • Promotes maintenance functions & conserves body energy

  • Promotes low blood pressure, low heart rate, & digestion

• Sympathetic

  • Fight or flight

  • Release epinephrine & norepinephrine

  • Increase heart rate

  • Increase blood pressure

  • Vasoconstriction

  • Increase blood sugar

What are the two parallel stress pathways?