surface area

Animal Form and Function Study Notes

Class Goals

• Explore the relationship between structure and function at different levels (from molecular to organism levels).

• Examine the impact of body size on physiology; Surface area versus volume considerations.

• Develop an understanding of "Homeostasis":

  • Maintenance of a constant internal environment.

  • Achieved by systems that sense changes in internal conditions and trigger responses that return conditions to normal.

  • Example: Thermoregulation.

Point-To-Ponder

How Does Body Size Affect Physiology?

• Compare pros and cons of large body size versus small body size.

Surface Area vs. Volume

Definitions and Relevance

• Surface Area: The total area that the surface of an object occupies.

• Volume: The amount of space that a substance (solid, liquid, gas) occupies.

• Relevance in Physiology:

  • The rate at which oxygen and nutrients diffuse into the cell and waste products diffuse out depends on the surface area available for diffusion.

  • The rate at which nutrients are used or wastes produced depends on the volume of the cell.

Worksheet on Body Size

Surface Area to Volume Calculator

• As cube side length increases, surface area and volume increase exponentially while the SVR decreases exponentially.

Metabolism and Body Size

Metabolic Rate

• The overall rate of energy consumption by an individual is defined as metabolic rate.

• Basal Metabolic Rate (BMR):

  • The rate at which an animal consumes oxygen while at rest, with an empty stomach, under normal temperature and moisture conditions.

  • BMR can be calculated as:
    ext{BMR} = \frac{\text{mL of O}_2 \text{ consumed}}{\text{gram of body mass} \times \text{hour}}

Implications of Body Size on BMR

• On a per-gram basis, smaller animals have higher BMRs than larger animals.

  • Example: An elephant has more mass than a mouse, but a gram of elephant tissue consumes less energy than a gram of mouse tissue.

• As an organism's size increases, its mass-specific metabolic rate must decrease to allow adequate surface area for material exchange.

Structural Adaptations for Optimal SA:V Ratios

Point-To-Ponder

• Consider specific organs that benefit from optimal surface area-to-volume ratios.

• Identify structural adaptations that increase surface area.

Homeostasis

Definition

• The stability in the chemical and physical conditions within an animal’s cells, tissues, and organs.

• Internal and physical states are maintained within a tolerable range despite surrounding environmental changes.

Types of Homeostasis

• Conformational Homeostasis: Achieved by the body passively matching conditions of a stable external environment.

• Regulatory Homeostasis: Achieved by active physiological processes triggered by variations in the internal or external environments.

Examples of Regulated Processes

Point-To-Ponder

• What are examples of conditions or processes that need to be regulated in animals?

  • Blood pressure

  • Blood glucose

  • Blood oxygen concentration

  • Blood pH

  • Body temperature

  • Water content (osmoregulation)

The Role of Regulation and Feedback

Homeostatic Mechanisms

• Many animals have regulatory systems that constantly monitor internal conditions (temperature, blood pressure, blood pH, blood glucose).

• Each variable has a set point (or set range) which is a normal or target value.

• If a variable changes, the homeostatic system acts quickly to modify it and re-establish homeostasis.

Components of a Homeostatic System

1. Sensor: Senses the internal or external environment; records a parameter.

2. Integrator: Evaluates incoming sensory information; compares sensor input with set-point and instructs effector.

3. Effector: Responds to restore the desired internal condition; changes parameter to return to the original range.

Thermoregulation

Importance

• Heat exchange is crucial because excessive heat or cold can result in death.

  • Effects of Heat: Proteins denature; dehydration occurs.

  • Effects of Cold: Slowed enzyme function and energy production.

Mechanisms of Heat Exchange

• Animals exchange heat with their environment through four ways (methods not listed in provided text).

Thermoregulatory Feedback

• Behavioral and physiological responses work towards returning body temperature toward the set point through negative feedback.

• Feedback systems work in antagonistic pairs—one set of responses increases and another set decreases the parameter.

Mechanisms of Temperature Regulation in Mammals

Feedback Loop - Negative Feedback

• Sensors: Record temperature (skin, spinal cord, anterior hypothalamus).

• Effectors' Actions:

  • If body temperature is above the set point:

  1. Blood vessels near the skin dilate; blood flow increases, enhancing heat loss from skin.

  2. Sweat glands are stimulated; evaporation results in heat loss.

  3. Respiratory centers stimulate panting for heat loss.

  • If body temperature is below the set point:

  1. Blood vessels near the skin constrict; blood flow is reduced, decreasing heat loss.

  2. Shivering generates heat in muscles.

  3. Chemical signals stimulate increased cellular respiration and heat production.

Causes of Temperature Variations

Causes of High Body Temperature

• Infections

• Overdose of certain medicines

• Excessive consumption of stimulant drugs (cocaine, amphetamines)

• Overactive thyroid (increased metabolic rate)

• Strenuous physical activity

• Conditions like seizures, agitation, or alcohol/drug withdrawal

Causes of Low Body Temperature

• Alcohol abuse (affects temperature regulation)

• Anesthesia effects

• Drug abuse

• Certain medications

• Low iodine/hypothyroidism

• Shock

• Sepsis (excess bacteria in the bloodstream)

• Chronic conditions (anemia, hepatitis C)

• Addison's Disease (lack of adrenal gland hormones)

Countercurrent Heat Exchangers

Mechanism Overview

• Some animals conserve heat with countercurrent heat exchangers, transferring heat from arteries to veins that lie parallel to each other.

• Efficient because they maintain a temperature gradient along their entire length.

  • Larger surface area = Larger overall temperature gradient.

• Related concepts: Countercurrent multipliers.

Water Balance

Principles

• Water Intake = Water Loss

• Necessary to sustain balanced concentrations of electrolytes throughout the body, keeping cells and tissues in favorable conditions.

Osmoregulation & Osmotic Stress

Definitions

• Diffusion: Movement of substances from regions of higher to lower concentration.

• Osmosis: The movement of water from regions of higher water concentration to regions of lower water concentration across a selectively permeable membrane.

• Related terms include osmolarity, osmotic stress, and osmoregulation.

Factors Affecting Diffusion

• Size and charge impact the rate of diffusion across a membrane:

  • Hydrophobic molecules: O2, CO2, N2

  • Small, uncharged polar molecules: H₂O, indole, glycerol

  • Large, uncharged polar molecules: Glucose, sucrose

  • Ions: Cl–, K+, Na+

Concentration Gradients

Assessing Diffusion Directions

• Determine if situations represent concentration gradients and their respective diffusion movements (left, right, or none).

Types of Solutions

Point-To-Ponder

• Provide examples of solutions that are:

  • Hypotonic: Lower concentration of solutes compared to another solution.

  • Hypertonic: Higher concentration of solutes compared to another solution.

  • Isotonic: Same concentration of solutes compared to another solution.

Osmoregulation in Marine Organisms

Osmoconformers

• Sponges and jellyfish do not need to osmoregulate; they are isotonic to seawater, which is a constant ionic and osmotic environment matching the electrolyte concentrations within these animals.

Osmotic Stress

Function

• Occurs when concentrations of dissolved substances in a cell or tissue are abnormal.

  • Osmoregulators: Organisms that regulate osmolarity inside their bodies to achieve homeostasis.

Cell Mechanisms for Elevators

Movement of Electrolytes

• Channels: Selectively admit specific ions.

• Carriers: Bind specific ions or molecules and transport them across the membrane by undergoing conformational changes.

Active Transport in Cells

• Plant and animal cells set up strong electrochemical gradients (typically Na+ in animals and H+ in plants), which are used to transport additional substances without requiring extra energy.

Shark Research

Osmoregulation Model

1. Na+/K+-ATPase establishes an electrochemical gradient.

2. Na+, Cl–, and K+ can enter the cell without additional energy expenditure (powered by the Na+ gradient).

3. Chloride channels enable Cl– to diffuse into gland lumens following their concentration gradient.

Causes & Consequences of Electrolyte Imbalance

Point-To-Ponder

• Examples include dehydration and electrolyte disorders.

The Kidney

Anatomy and Function

• The renal artery brings blood containing nitrogenous wastes into the kidney; the renal vein carries cleaned blood away.

• Urine is transported via the ureter to the bladder (storage) and then to the surface via urethra for excretion.

Nephron Overview

• Nephron: The functional unit of the kidney that produces urine by removing waste and excess substances from blood.

  • Contains approximately 1,000,000 nephrons in each human kidney.

Structures of the Nephron

• Bowman’s Capsule: Surrounds the glomerulus.

• Glomerulus: Capillary cluster that brings blood from the renal artery to the nephron, featuring large pores to filter substances.

Urine Formation

Steps

1. Ultrafiltration: Fluid seeps from glomerular capillaries into the Bowman’s capsule, forming pre-urine.

2. Reabsorption: Occurs along the nephron where valuable small substances (e.g., glucose, vitamins, amino acids) are recovered.

3. Secretion: Additional waste products are secreted from blood into the tubule.

Distinct Regions of the Nephron

1. Proximal Tubule (PT): Selectively reabsorbs useful substances.

2. Loop of Henle (LOH): Establishes osmotic gradient in tissue.

3. Distal Tubule (DT) and Collecting Duct (CD): Regulate water retention and electrolyte balance.

Hormonal Controls

• Aldosterone:

  • Hormone that stimulates the kidney to retain sodium and water.

  • If Na+ levels are low, aldosterone releases sodium pumps, enhancing sodium reabsorption.

• ADH (Antidiuretic Hormone):

  • Triggers aquaporin insertion into the apical membranes of cells.

  • Increases permeability to water, enhancing water reabsorption and urine concentration.

Summary Table of the Nephron Structure and Function

Central Nervous System Responses

Loss of Water

• ADH Release: Increased tubular reabsorption of water to dilute body fluids.

  • Thirst Behavioral Response: Increased intake of water.

Inhibition of ADH

• Loss of water leads to decreased serum toxicity, influencing the behavioral response for water intake.

Questions for Reflection

Point-To-Ponder

• What symptoms are expected in individuals with defective forms of ADH or aquaporins?

These structured notes provide a comprehensive understanding of animal physiology, focusing on the interplay between size, metabolism, homeostasis, and the intricate processes of the kidneys. The formatting allows for easy navigation of concepts and key definitions, making it suitable for replacement of the original source material.