Biology Chapter on Digestion and Absorption

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Questions and Answers

What are the end products of maltose digestion?

1 glucose + 1 lactose

1 glucose + 1 fructose

2 glucose molecules (correct)

1 galactose + 1 glucose

Which enzyme is responsible for the digestion of sucrose?

Lactase

Amylase

Sucrase (correct)

Maltase

How are most proteins absorbed after digestion?

As tripeptides

As small peptides

As larger polypeptides

As free amino acids (correct)

Which transport protein is responsible for the absorption of glucose and galactose in the intestinal mucosa?

SGLT Signup and view all the answers

What happens to peptides larger than tripeptides during absorption?

They are absorbed through transcytosis. Signup and view all the answers

Lactose is broken down into which two monosaccharides?

Glucose and galactose Signup and view all the answers

Which enzyme breaks down lactose?

Lactase Signup and view all the answers

What type of bond is primarily present in proteins?

Peptide bonds Signup and view all the answers

What type of hormones does the endocrine portion of the pancreas secrete?

Insulin and glucagon Signup and view all the answers

What role does bicarbonate play in the digestive process?

Neutralizes gastric acid Signup and view all the answers

Which enzyme is activated by enteropeptidase?

Trypsinogen Signup and view all the answers

What is the primary function of pancreatic lipase?

Hydrolyzes triglycerides into fatty acids and monoglycerides Signup and view all the answers

What process occurs first when large fat droplets enter the small intestine?

Bile salts emulsifying the fats Signup and view all the answers

Where do chylomicrons transport absorbed fats after their formation?

To the vena cava Signup and view all the answers

What is the role of colipase in fat digestion?

Interacts with pancreatic lipase Signup and view all the answers

In the digestion of fats, what do monoglycerides and fatty acids do after moving out of micelles?

Enter the cells of the small intestine Signup and view all the answers

What are the end products of lipases digesting triglycerides?

Glycerol and fatty acids Signup and view all the answers

In glycolysis, what substance does glycerol become?

Glycolysis substrate Signup and view all the answers

What process chops 2-carbon acyl units off the fatty acids?

Beta-oxidation Signup and view all the answers

What can the acyl units be converted into for use in the citric acid cycle?

Acetyl CoA Signup and view all the answers

Where does β-oxidation occur within the cell?

Mitochondrial matrix Signup and view all the answers

What is released as a byproduct during β-oxidation?

CO2 Signup and view all the answers

How many fatty acids does one triglyceride molecule yield after digestion?

3 Signup and view all the answers

In which cycle can acetyl CoA be utilized after its formation from acyl units?

Citric Acid Cycle Signup and view all the answers

What is the primary function of buffer systems in the body?

To moderate changes in pH Signup and view all the answers

Which statement correctly describes the role of intercalated cells in the collecting duct during alkalosis?

They reabsorb HCO3- and K+ while excreting H+ Signup and view all the answers

Which of the following disturbances in volume is most likely to cause a decrease in osmolarity?

Drinking a large amount of water Signup and view all the answers

What percentage of pH disturbances can ventilation correct?

75% Signup and view all the answers

Which renal mechanism is utilized to buffer changes in pH?

Use of ammonia and phosphate buffers Signup and view all the answers

What occurs during hypoventilation in relation to acid-base balance?

Increased carbon dioxide retention Signup and view all the answers

What causes volume and osmolarity to remain unchanged?

Replacement of sweat loss with isotonic saline Signup and view all the answers

What is a characteristic feature of Type 1 diabetes mellitus?

Autoimmune destruction of beta cells Signup and view all the answers

Which condition is indicated by fasting blood glucose levels greater than 125 mg/dL?

Diabetes mellitus Signup and view all the answers

What is the primary role of the kidneys in acid-base balance?

To utilize ammonia and phosphate buffers Signup and view all the answers

What role does HCO3- play in the Type A intercalated cells of the collecting duct?

It acts as a buffer to lower [H+]. Signup and view all the answers

What measurement indicates prediabetes after a glucose tolerance test?

140 – 199 mg/dL Signup and view all the answers

What is the significance of ATP in the process occurring in the Type B intercalated cells?

It is used to reabsorb HCO3-. Signup and view all the answers

What is the effect of low insulin levels in the context of glucose metabolism?

Increased blood glucose levels Signup and view all the answers

Which body systems can be affected by complications from diabetes mellitus?

Blood vessels, eyes, kidneys, and nervous system Signup and view all the answers

What happens to K+ in Type A intercalated cells when [H+] is high?

K+ is excreted in urine. Signup and view all the answers

How does H2O + CO2 contribute to the function of Type A intercalated cells?

It is converted to HCO3- to decrease blood pH. Signup and view all the answers

What role does hexokinase play in glucose metabolism?

It converts glucose to glucose 6-phosphate Signup and view all the answers

What defines hyperglycemia in diabetes mellitus?

Abnormally elevated plasma glucose concentrations Signup and view all the answers

What characteristic distinguishes the luminal fluid of Type B intercalated cells?

It has low [H+]. Signup and view all the answers

Why is Cl- relevant in the context of Type A intercalated cells?

It enhances the reabsorption of K+. Signup and view all the answers

Which of the following tests is NOT used to diagnose diabetes?

Lipid profile test Signup and view all the answers

In which scenario would H+ be predominantly excreted in urine?

When there is a high production of HCO3-. Signup and view all the answers

How does the presence of high [K+] affect the Type A intercalated cells?

It promotes the formation of HCO3-. Signup and view all the answers

Study Notes

Human Physiology Test #4 Review

Nephron Structure:
- Some nephrons extend deep into the medulla.
- The cortex contains Bowman's capsules, proximal, and distal tubules.
- The medulla contains loops of Henle and collecting ducts.
- One nephron has two arterioles and two sets of capillaries forming a portal system (afferent and efferent arterioles, glomerulus, peritubular capillaries, and vasa recta).
- The juxtaglomerular apparatus is also part of the nephron.

Glomerular Filtration Rate (GFR)

Filtration Pressure:
- GFR is determined by the balance of hydrostatic pressure (blood pressure) and colloid osmotic pressure, and capsule fluid pressure.
- Filtration pressure depends on blood pressure and opposes colloid osmotic pressure and capsule fluid pressure, with the difference being the net filtration pressure.
GFR Regulation:
- GFR is relatively constant at a blood pressure of 80-180 mm Hg.
- GFR is regulated primarily by altering blood flow through the renal arterioles.
- Increased resistance in the afferent arteriole decreases GFR.
- Increased resistance in the efferent arteriole increases GFR.
- Decreased resistance in the afferent arteriole increases GFR, and decreases in the efferent arteriole decreases GFR.

Reabsorption

Types of Reabsorption:
- Reabsorption can be active or passive.
- Transcellular transport involves substances crossing the apical and basolateral membranes of the tubule epithelial cells.
- Paracellular transport involves substances passing through cell-cell junctions between adjacent cells.
Active Transport of Na+:
- Creates an electrical gradient.
- Anions follow Na+ which creates an osmotic gradient.
- Water follows, leaving behind a higher concentration of cations.
- Cations move down concentration gradients.
- Exchangers (NHE) and pumps (Na+-K+-ATPase) are involved.

Saturation of Renal Transport

Saturation:
- Saturation is the maximum transport rate when all carriers are occupied by substrate.
Transport Maximum (Tm):
- The transport rate at saturation.
Renal Threshold:
- The plasma concentration of a substance at which it first appears in urine.
Glucose and other related factors:
- Glucose in urine is also called glucosuria or glycosuria.
- Peritubular capillary pressures favor reabsorption.

Secretion

Definition:
- Active movement of molecules from the extracellular fluid into the nephron lumen.
Importance:
- Secretion is important in homeostasis, specifically for K+ and H+.
- Increasing secretion increases nephron excretion.

Excretion

Definition:
- Excretion is the sum of filtration minus reabsorption, plus secretion in the kidneys.
Clearance:
- Clearance is the rate at which a solute disappears from the body by excretion or metabolism.
- Clearance of X = excretion rate of X/[X]plasma, expressed as ml plasma/min cleared of X.
Key Substances:
- Inulin is a plant polysaccharide that freely filters but neither reabsorbed or secreted and used to measure GFR
- Creatinine is a breakdown product of phosphocreatine, its production and breakdown are relatively constant, but some secretion occurs in the urine.

Glomerular Filtration, Reabsorption and Excretion

Renal Handling: how a substance is dealt with by the kidneys.
Relationship: how filtration, reabsorption, and excretion of a substance relate to each other.
Inulin clearance is equal to GFR. Glucose is normally completely reabsorbed.

Volume and Pressure Regulation

Responses to Decreased/Elevated Volume and Pressure
- Volume receptors in the atria and carotid/aortic baroreceptors stimulate homeostatic reflexes.
- Cardiovascular system responds with changes in cardiac output and vasoconstriction or vasodilation, in order to stabilize blood volume and pressure.
- Kidneys respond by excreting salts and water to adjust ECF volume.
- Thirst and water consumption are also triggered.

Osmolarity Changes Through the Nephron

Fluid Flow Changes: Fluid progressively becomes more concentrated as it passes through the descending limb of the loop of Henle, and into the collecting duct.
Regulation: Variable reabsorption of water and solutes in the nephron sections are under hormonal control.

Vasopressin in Water Permeability

Actions: Vasopressin leads to insertion of water pores (aquaporins) into the apical membrane of the collecting duct cells.
Mechanism: Vasopressin binds to receptors, activating a cAMP second messenger system and triggering the insertion of aquaporins.

Renin-Angiotensin Pathway

Renin-Angiotensin System (RAS): Controls blood pressure.
Juxtaglomerular Cells: Secrete renin when blood pressure falls.
Renin's Action: Converts angiotensinogen into angiotensin I.
ACE (Converting Enzyme): Converts angiotensin I to angiotensin II.
Angiotensin II's Role: Potent vasoconstrictor; raises blood pressure. This leads to a cascade of responses.

Aldosterone

Primary Action: Aids in renal sodium reabsorption.
Stimuli: RAS pathway, increases in potassium concentration, and possibly other factors.
Regulation: It's released by the adrenal cortex in response to factors like potassium concentration, blood pressure.

Natriuretic Peptides

ANP and BNP: Peptides produced and released in response to elevated blood volume or stretch of heart chambers.
Effects: Influence kidney function by promoting sodium and water excretion, reduce blood volume, pressure.

Acid-Base Disturbances & Intercalated Cells

Intercalated cells: specialized cells in the collecting duct that help maintain acid-base balance. (Type A and Type B)
Acidosis: Type A intercalated cells actively excrete hydrogen ions.
Alkalosis: Type B intercalated cells actively excrete bicarbonate ions.

Diabetes Mellitus

Diabetes Mellitus: Characterized by high plasma glucose.
Types: Type 1 (insulin deficiency), Type 2 (insulin resistance).
Complications: Affect blood vessels, eyes, kidneys.
Diagnosing Diabetes: Blood glucose measurements (fasting, glucose tolerance tests).

Metabolism

Anabolism: Constructing larger molecules from smaller ones.
Catabolism: Breaking larger molecules into smaller ones.
Fed State/Absorptive State: After eating, glucose and other nutrients are absorbed and used.
Fasting State/Postabsorptive State: In the absence of food, the body breaks down stored nutrients to meet its energy demands.

Fasted State Metabolism

Glycogenolysis: Breakdown of glycogen (stored glucose) to release glucose.
Lipolysis: Breakdown of triglycerides to produce fatty acids and glycerol.
Protein Breakdown: Deamination to produce amino acids and energy.
Acetyl CoA: Important intermediate in ATP production.
Ketone Bodies: Produced when acetyl CoA can not be fully processed.

Digestion, Absorption: Fats, Carbohydrates & Proteins

Fats: Bile salts emulsify fats, pancreatic lipase breaks down fats, absorbed as monoglycerides/fatty acids and chylomicrons.
Carbohydrates: Starch/glycogen broken into monosaccharides by amylase and/or specific enzymes, absorbed into the blood.
Proteins: Endopeptidases act at internal peptide bonds, exopeptidases at terminal peptide bonds. Absorbed as amino acids following digestion.

Energy Storage

Fat and Glycogen: Provide energy storage in the body.
Glycogen: The body's readily available energy source.
Fat: Long-term energy storage, contains more energy, but slower to access.

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Description

Test your knowledge on the digestion process, including enzymes, absorption mechanisms, and the end products of carbohydrate and protein digestion. This quiz covers key concepts in the digestion of carbohydrates, proteins, and fats, focusing on the biochemical pathways involved in nutrient absorption.