biology 120 module 5+6 review

Biology 120: Modules 5 +6

Summary of Diabetes Mellitus and Hormonal Regulation

Chemical Messengers and the Endocrine System:

- Chemical messengers are classified into autocrine (affecting the same cell), paracrine (affecting nearby cells), neurotransmitters (secreted by neurons), and endocrine (hormones secreted into the blood to affect distant cells).

- Hormones are secreted into the bloodstream by ductless glands and affect specific target cells.

- Hormones interact with receptors, which can be membrane-bound (for faster cell responses) or intracellular (for slower, gene-related changes). The mechanism of action involves hormone-receptor interaction leading to cellular changes like signal amplification or gene expression.

Types of Hormones:

1. Peptide/Polypeptide Hormones: Water-soluble, bind to surface receptors.

2. Steroid Hormones: Lipid-soluble, pass through cell membranes to bind intracellular receptors.

3. Amine Hormones: Derived from amino acids, can be either water or fat-soluble.

Glucose Homeostasis and Insulin:

- Insulin and glucagon are key hormones from the pancreas regulating blood glucose levels.

  - Insulin promotes glucose uptake into cells, stimulating glycogenesis in the liver and muscle, and fat storage in adipose tissue.

  - Glucagon triggers glycogen breakdown (glycogenolysis) to release glucose when blood sugar is low.

- GLUT transporters enable glucose entry into cells, with some being regulated by insulin (e.g., GLUT 4 in muscle and fat cells).

Diabetes Mellitus:

- Type 1 Diabetes: Caused by immune system destruction of insulin-producing beta cells in the pancreas.

- Type 2 Diabetes: Characterized by insulin resistance, where cells do not respond properly to insulin. This is primarily linked to lifestyle factors (obesity, poor diet, lack of exercise) and genetic predisposition.

Chronic Hyperglycemia Complications:

- Macrovascular complications: Atherosclerosis, leading to heart attack, stroke, and peripheral artery disease.

- Microvascular complications: Diabetic nephropathy (kidney damage) and diabetic retinopathy (retinal damage, leading to blindness).

- Neuropathy: Nerve damage due to reduced blood flow, leading to loss of sensation and increased injury risk.

Treatment Approaches:

- Pharmaceuticals: Drugs like metformin, GLP-1 agonists, and sulfonylureas help manage blood glucose levels.

- Lifestyle changes: Diet (controls blood glucose) and exercise (stimulates GLUT 4 insertion and improves insulin sensitivity) are crucial.

In summary, diabetes is a significant public health concern due to its impact on glucose regulation, leading to severe complications. Insulin and other hormones play a critical role in maintaining glucose homeostasis, and interventions like medication and lifestyle changes are vital for managing the disease.

Summary: Antarctic Icefish and Their Survival Without Red Blood Cells

Blood Functions:

Blood plays several vital roles in the body, including:

- Transporting gases (O2, CO2)

- Fighting infections and aiding in coagulation

- Transporting heat, waste, hormones, and nutrients

Gas Exchange and Red Blood Cells (RBCs):

- Gas exchange occurs at the respiratory surface, where thin membranes and numerous capillaries allow efficient O2 and CO2 diffusion.

- RBCs contain hemoglobin (Hb), a protein that binds O2 and increases its transport capacity in the blood. Hemoglobin binds O2 reversibly through cooperative binding, meaning as one O2 molecule binds, it increases the affinity for additional O2 molecules.

- Hemoglobin's affinity for O2 is influenced by O2 concentration: high O2 leads to high binding affinity (loading at the lungs), and low O2 leads to decreased affinity (unloading at tissues).

Other Respiratory Pigments:

- Myoglobin (Mb) is another oxygen-binding protein found in muscles, providing O2 storage and release under low O2 conditions. Some icefish lack myoglobin as well.

Circulatory System:

- Fish have a two-chambered heart and a closed circulatory system with capillaries for gas exchange. Blood pressure is relatively low, and blood flow through capillaries is slow to maximize gas exchange.

Icefish and Loss of Hemoglobin:

- Icefish (a type of fish in the Antarctic) have evolved to survive without hemoglobin (Hb), which is unusual because it is typically crucial for oxygen transport.

- Icefish lost the ability to produce hemoglobin due to a gene deletion (loss of globin genes) that occurred around 2-5.5 million years ago.

- Despite this loss being considered a disadaptation (a trait that is inferior to ancestral traits), it persists in icefish due to environmental factors. Cold water in the Antarctic has higher oxygen content, and icefish live in well-aerated, low-temperature environments, reducing their metabolic rate and oxygen demand.

Advantages and Trade-offs:

- The cold, oxygen-rich environment allows icefish to survive without hemoglobin, as they can absorb enough oxygen directly from the water.

- However, the loss of hemoglobin limits the fish's thermal tolerance and gives it a disadvantage in warmer or less oxygen-rich environments.

- Icefish also face less competition, which may have helped them persist in this unique condition, although this trait is not advantageous in the context of competition with other species.

In summary, icefish survive without red blood cells and hemoglobin due to the high oxygen availability in cold Antarctic waters and their low metabolic needs. The loss of hemoglobin is a result of evolutionary changes in their genes, and while it is disadvantageous in some contexts, it has persisted due to environmental factors.

Summary: Diabetes Mellitus and Icefish Survival Without Red Blood Cells

Blood Functions and Gas Exchange:

Blood serves several vital functions in the body, including transporting gases (O2, CO2), fighting infections, clotting, transporting heat, nutrients, and waste. Oxygen is crucial for cellular respiration, where glucose and oxygen are used to produce ATP and energy. Gas exchange occurs at the respiratory surface, where thin membranes and capillaries facilitate efficient O2 and CO2 diffusion.

Red blood cells (RBCs) play a central role in transporting oxygen through hemoglobin (Hb), a protein that binds O2 reversibly. Hb’s affinity for O2 is influenced by O2 concentration: it readily binds O2 when oxygen levels are high (in the lungs) and releases it when levels are low (in the tissues). Myoglobin (Mb), another oxygen-binding protein found in muscles, stores oxygen for use during low oxygen conditions.

Endocrine Regulation of Glucose and Hormones:

Insulin and glucagon, two key hormones from the pancreas, regulate blood glucose levels. Insulin promotes glucose uptake by cells, stimulates glycogenesis in the liver and muscles, and aids fat storage in adipose tissue. Glucagon triggers glycogen breakdown (glycogenolysis) when blood sugar is low.

Glucose transport across cell membranes is facilitated by GLUT transporters. Some GLUT transporters, like GLUT 4, are insulin-regulated and are inserted into the membrane when insulin binds to its receptor. These transporters are essential for glucose uptake in muscle and fat cells.

Diabetes Mellitus:

Diabetes, a disorder of glucose regulation, comes in two types:

- Type 1 Diabetes: Caused by the immune system attacking insulin-producing beta cells in the pancreas.

- Type 2 Diabetes: Characterized by insulin resistance, where cells do not respond properly to insulin. It is influenced by lifestyle factors (obesity, poor diet, lack of exercise) and genetic predisposition.

Chronic hyperglycemia (high blood glucose) leads to severe complications:

- Macrovascular complications (e.g., atherosclerosis) affect large blood vessels, reducing blood flow and leading to heart attack, stroke, and peripheral artery disease.

- Microvascular complications (e.g., diabetic nephropathy and retinopathy) damage small capillaries in the kidneys and retina, leading to kidney disease and blindness.

- Neuropathy occurs when reduced blood flow damages nerves, causing loss of sensation and higher injury risk.

Treatment for diabetes includes pharmaceuticals (e.g., metformin) to improve insulin sensitivity and lifestyle changes (diet and exercise) to manage blood glucose levels.

Icefish and Hemoglobin Loss:

Unlike most fish, icefish in the Antarctic lack hemoglobin in their blood. This unusual adaptation is due to the loss of functional globin genes (responsible for producing hemoglobin), which occurred around 2-5.5 million years ago. This loss is considered a disadaptation (a trait less advantageous than the ancestral trait), but it persists in icefish due to environmental factors.

In cold Antarctic waters, oxygen content is higher, and icefish have a low metabolic rate, reducing their oxygen demand. The well-aerated, cold environment provides enough oxygen directly from the water for the fish to survive. Although the loss of hemoglobin limits their thermal tolerance, icefish thrive in these conditions with minimal competition, allowing the trait to persist.

In summary, the survival of icefish without red blood cells is linked to the unique oxygen-rich and cold Antarctic environment, while diabetes is a major public health concern due to its impact on glucose regulation and the potential for severe complications. Hormonal regulation, like insulin and glucagon in glucose homeostasis, is crucial for maintaining health, just as evolutionary adaptations, like hemoglobin loss in icefish, help them survive in extreme environments.

### Study Guide: Understanding Diabetes Mellitus and the Physiology of Icefish

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#### 1. Features of the Diabetes Mellitus Epidemic

- Prevalence: Increasing cases of diabetes, particularly Type 2, driven by lifestyle factors such as poor diet, obesity, and lack of exercise.

- Public Health Concern: Type 2 diabetes is a major issue due to its high rates, complications, and healthcare burden.

- Complications: Chronic hyperglycemia leads to macrovascular (heart disease, stroke) and microvascular (diabetic retinopathy, nephropathy) complications, as well as neuropathy.

#### 2. Chemical Messengers and Hormones

- Hormones: Chemical messengers that travel through the bloodstream to target distant cells to regulate various physiological processes.

  - Hormones vs. Other Messengers: Unlike neurotransmitters (short-range) or autocrine/paracrine messengers (local), hormones have long-distance effects.

  - Hormone Characteristics: Secreted into the blood, travel to target cells, and cause a specific response.

#### 3. Types of Hormones

- Steroid Hormones: Derived from cholesterol (e.g., cortisol, estrogen), lipid-soluble, can pass through cell membranes and bind to intracellular receptors.

- Protein Hormones (Peptide/Polypeptide): Water-soluble, bind to receptors on the surface of target cells (e.g., insulin, glucagon).

- Amino Acid Derivative Hormones: Modified amino acids (e.g., thyroid hormones, catecholamines), can be either water- or lipid-soluble.

#### 4. Membrane-Bound vs. Intracellular Receptors

- Membrane-Bound Receptors: Located on the cell surface, bind water-soluble hormones (e.g., peptide hormones) and initiate signal transduction pathways (e.g., cAMP or phosphorylation). They cause rapid cell changes, often involving ATP.

- Intracellular Receptors: Located inside the cell, bind lipid-soluble hormones (e.g., steroid hormones) and regulate gene expression, leading to slower, long-term changes.

#### 5. Mechanism of Action of Hormones

- Membrane Receptors: Trigger a cascade of intracellular events, often amplifying the signal (e.g., insulin binding stimulates glucose uptake).

- Intracellular Receptors: Bind to DNA and affect gene transcription, influencing protein production and cell function over time.

#### 6. Insulin and Glucagon in Glucose Homeostasis

- Insulin: Secreted by beta cells of the pancreas when blood glucose is high. It promotes glucose uptake by cells, glycogenesis in the liver and muscles, and fat storage in adipose tissue.

- Glucagon: Secreted by alpha cells of the pancreas when blood glucose is low. It stimulates glycogen breakdown (glycogenolysis) and releases glucose into the bloodstream.

#### 7. Alterations in Insulin Secretion/Action

- Type 1 Diabetes: Caused by the destruction of insulin-producing beta cells (immune attack).

- Type 2 Diabetes: Insulin resistance, where cells do not respond properly to insulin, often due to obesity or lifestyle factors.

- Effect on Blood Glucose: In both types, glucose regulation is impaired, leading to high blood sugar levels.

#### 8. Facilitated Diffusion and Glucose Transport

- Facilitated Diffusion: Movement of glucose across cell membranes via GLUT transporters (membrane proteins), which aid in passive transport.

- Regulated vs. Non-Regulated Transporters:

  - Regulated (e.g., GLUT4): Insulin stimulates the insertion of GLUT4 transporters into the membrane in muscle and adipose tissue.

  - Non-Regulated (e.g., GLUT1, GLUT2, GLUT3): Present in the membrane at all times, no insulin signal required.

#### 9. Actions of Insulin on Liver, Muscle, and Adipose Tissue

- Liver: Stimulates glucose uptake (via GLUT2) and glycogenesis, converting glucose to glycogen.

- Muscle: Stimulates GLUT4 insertion, glucose uptake, glycogenesis, and protein synthesis.

- Adipose Tissue: Stimulates GLUT4 insertion, glucose uptake, and fat storage (triglyceride production).

#### 10. Type 1 vs. Type 2 Diabetes

- Type 1 Diabetes: Insulin deficiency due to beta cell destruction.

- Type 2 Diabetes: Insulin resistance, where cells do not respond to insulin properly.

#### 11. Insulin Resistance in Type 2 Diabetes

- Insulin Resistance: Cells become less responsive to insulin. From an endocrine signaling perspective, this means the signal (insulin) cannot effectively induce glucose uptake or metabolic processes in target cells.

#### 12. Health Consequences of Chronic Hyperglycemia

- Macrovascular Complications: Atherosclerosis, leading to heart disease, stroke, and peripheral artery disease.

- Microvascular Complications: Diabetic nephropathy (kidney damage) and diabetic retinopathy (vision problems due to retina damage).

- Neuropathy: Nerve damage due to poor blood supply, leading to loss of sensation and increased risk of injury.

#### 13. Treatment of Type 2 Diabetes

- Pharmaceuticals: Medications like metformin, GLP-1 agonists, and sulfonylureas help regulate glucose by increasing insulin sensitivity or stimulating insulin release.

- Lifestyle Changes: Diet and exercise improve glucose uptake, especially via GLUT4 transporters.

  - Exercise: Increases insulin sensitivity, promoting GLUT4 insertion into muscle cells.

#### 14. Unique Features of Antarctic Icefish

- Lack of Hemoglobin: Icefish lack red blood cells and hemoglobin, a trait rare among vertebrates.

- Adaptation to Cold: Cold Antarctic waters have high oxygen content, reducing the fish's metabolic demand, allowing survival without hemoglobin.

#### 15. Blood and Red Blood Cells (RBCs)

- General Functions of Blood: Gas transport, immune function, nutrient transport, waste removal, hormone transport, and temperature regulation.

- RBCs: Carry oxygen via hemoglobin, facilitating gas exchange and oxygen delivery to tissues.

#### 16. Respiratory Pigments in Oxygen Transport

- Hemoglobin: A protein in RBCs that binds O2 for transport. Its oxygen-binding capacity is influenced by oxygen concentration (PO2).

- Oxygen Affinity: The affinity of hemoglobin for oxygen can vary; a high affinity means it binds O2 readily, while low affinity means it releases O2 more easily. The P50 value measures the oxygen pressure at which hemoglobin is 50% saturated.

#### 17. Myoglobin vs. Hemoglobin

- Myoglobin: Found in muscle cells, it has a high affinity for oxygen and serves as an O2 reserve. It releases oxygen only when levels are very low.

- Hemoglobin: Found in red blood cells, transports oxygen throughout the body, and binds O2 reversibly.

#### 18. Blood Vessels in Closed Circulatory Systems

- Capillaries: Small, thin-walled blood vessels where gas exchange occurs. Their large cross-sectional area and slow blood flow facilitate efficient exchange.

- Cardiac Output (CO): The volume of blood pumped by the heart per unit of time, influenced by heart rate (HR) and stroke volume (SV).

#### 19. Icefish Hemoglobin Loss and Evolution

- Globin Gene Loss: Icefish lost the ability to synthesize hemoglobin due to a gene deletion that occurred 2-5.5 million years ago.

- Compensation Mechanisms: Icefish evolved to survive in cold, oxygen-rich Antarctic waters, where their lower metabolic rate and constant water movement provide sufficient oxygen.

#### 20. Importance of the Antarctic Habitat in Icefish Evolution

- Cold Water: Higher O2 content and lower metabolic demand allowed icefish to survive without hemoglobin.

- Evolutionary Persistence: Icefish's unique physiological traits, such as low thermal tolerance, have been maintained due to the stable environmental conditions of the Antarctic.

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Use this study guide to review key concepts related to diabetes, hormone signaling, glucose homeostasis, and the unique physiology of Antarctic icefish. Make sure to understand the mechanisms of action of hormones, insulin regulation, and the physiological adaptations of icefish to their environment.