Homeostasis, Endocrine Signaling, Animal Nutrition, Circulation & Gas Exchange

Regulating and Conforming

• Regulating: Internal mechanisms control internal change despite external fluctuation.

• Conforming: Internal condition changes with external changes.

• Animals may regulate some conditions and not others, like fish conforming to temperature but regulating blood solute concentrations.

• Feedback control maintains animal internal environment.

Thermoregulation

• Thermoregulation: Maintaining internal temperature within a tolerable range.

• Endothermic Animals:

  • Generate heat by metabolism (birds, mammals).

  • Maintain stable body temperature via behavior.

• Ectothermic Animals:

  • Gain heat from external sources (invertebrates, fishes, amphibians, nonavian reptiles).

  • Consume less food due to environmental heat source.

Homeostasis

• Homeostasis: Maintaining a “steady state” regardless of external environment.

• Achieving homeostasis:

  • Maintain variable at or near a set point.

  • Fluctuations trigger responses to return to set point (stimulus, sensor, response).

• Relies on negative feedback to reduce stimulus; regulated changes are essential (body temperature, blood pH, glucose concentration).

• Acclimatization in Thermoregulation: Birds and mammals vary insulation; ectotherms produce “antifreeze” compounds in subzero temperatures.

• Thermoregulation in mammals is controlled by the hypothalamus.

• Fever: result of change to set point for biological thermostat.

Circulatory Adaptations for Thermoregulation

• Alter blood flow between body core and skin in response to temperature changes.

• Vasodilation: Widening of superficial blood vessels promotes heat loss.

• Vasoconstriction: Narrowing of superficial blood vessels reduces heat loss.

• Countercurrent exchange in marine mammals and birds transfers heat between fluids flowing in opposite directions.

Coordination & Control of the Endocrine and Nervous Systems

• Hormones: Signaling molecules affect single or multiple locations; only cells with receptors respond; coordinates gradual changes.

• Nervous System: Nerve impulses travel along axons, connecting specific locations for immediate and rapid responses.

Coordination & Control of Endocrine and Nervous Systems

• pH level in duodenum relies on Endocrine Pathways: Acidic stomach contents stimulate endocrine cells to secrete secretin, raising pH in the duodenum via pancreas.

• Pancreas acts as exocrine gland (secreting substances through a duct) or endocrine gland (secreting hormones directly into interstitial fluid).

Coordination & Control of Endocrine and Nervous Systems

• Neuroendocrine Pathways: Respond to stimuli from the external environment via a sensor in the nervous system.

• Hypothalamus sends signals to pituitary gland, stimulating synthesis and release of hormones from the anterior pituitary.

• Posterior pituitary secretes oxytocin and antidiuretic hormone (ADH).

Coordination & Control of Endocrine and Nervous Systems

• Feedback Regulation in Endocrine Pathways: Loops link response back to stimulus.

  • Negative feedback dampens stimulus; positive feedback reinforces stimulus.

Coordination & Control of Endocrine and Nervous Systems

• Pathways of Water-Soluble and Lipid-Soluble Hormones:

  • Water-soluble hormones bind to cell-surface receptors, triggering signal transduction.

  • Lipid-soluble hormones have receptors inside cells, altering transcription of genes.

Coordination & Control of Endocrine and Nervous Systems

• Multiple Effects of Hormones: Hormones elicit more than one type of response due to differing receptors or response molecules (e.g., epinephrine).

Osmoregulation and Excretion in Many Animals

• Osmoregulation: Control of solute concentrations in interstitial fluid and balance of water gain and loss.

• Osmolarity: Solute concentration determines water movement across membranes.

  • Isoosmotic: equal water movement.

  • Differing Osmolarity: net flow from hypoosmotic to hyperosmotic solution.

• Osmoconformers: isoosmotic with surroundings (marine animals).

• Osmoregulators: expend energy to control water uptake and loss.

Osmoregulation and Excretion in Many Animals

• Marine and freshwater organisms have opposite challenges.

  • Marine fish drink seawater and excrete salt.

  • Freshwater fish drink almost no water and replenish salts.

• Land animals reduce water loss via body coverings; drink water, eat moist foods, produce water metabolically.

Osmoregulation and Excretion in Many Animals

• Nitrogenous Wastes: Affect water balance (breakdown products of proteins and nucleic acids).

• Ammonia ($NH_3$) excretion is common in aquatic organisms; vertebrates excrete urea (less toxic).

• Insects, land snails, and reptiles excrete uric acid (semisolid paste, energetically expensive).

Osmoregulation and Excretion in Many Animals

• Excretory Processes: Rely on transport epithelia.

• Urine production:

  • Filtration: filtering of body fluids.

  • Reabsorption: reclaiming valuable solutes.

  • Secretion: adding nonessential solutes and wastes.

  • Excretion: releasing processed filtrate.

Osmoregulation and Excretion in Many Animals

• Excretory Processes

• Vertebrates: kidneys consist of tubules in contact with capillaries; ducts carry urine out of the body.

From Blood Filtrate to Urine

• Bowman’s capsule: produces filtrate (salts, glucose, amino acids, vitamins, nitrogenous wastes).

• Proximal tubule: reabsorption of ions, water, and nutrients.

• Descending limb of the loop of Henle: reabsorption of water, filtrate becomes concentrated.

From Blood Filtrate to Urine

• Ascending limb of the loop of Henle: salt but not water moves out, filtrate becomes dilute.

• Distal tubule: regulates K+ and NaCl concentrations, contributes to pH regulation.

• Collecting duct: carries filtrate through medulla; reabsorption of water and nutrients, urine is hyperosmotic.

Hormones: Kidney Function, Water Balance, and Blood Pressure

• Concentrating Urine in the Mammalian Kidney: Water leaves descending limb, increasing filtrate osmolarity; salt diffuses from ascending limb, maintaining high osmolarity in medulla.

• Filtrate in ascending limb is hypoosmotic and descends to collecting duct, water is extracted, concentrating solutes.

Homeostatic Regulation of the Kidney

• Nervous and hormonal inputs regulate kidney function, affecting blood pressure and volume.

• Increased blood osmolarity triggers Antidiuretic hormone (ADH) release, conserving water; decreased osmolarity drops ADH secretion.

Homeostatic Regulation of the Kidney

• The Renin-Angiotensin-Aldosterone System (RAAS) regulates kidney function.

• A drop in blood pressure causes juxtaglomerular apparatus (JGA) to release renin, forming angiotensin II.

• Angiotensin II raises blood pressure, decreases blood flow to kidneys, and stimulates aldosterone release, increasing blood volume and pressure.

Animal Nutrition

• Diet must supply chemical energy, organic molecules, and essential nutrients.

• Provides ATP, organic building blocks, and essential nutrients (amino acids, fatty acids, vitamins, minerals).

• Fatty acids are converted into membrane phospholipids, signaling molecules, and storage fats.

• Plant proteins are often incomplete.

Animal Nutrition

• Vitamins: Organic molecules required in small amounts (fat-soluble and water-soluble).

• Minerals: Inorganic nutrients, usually required in small amounts; excess impairs homeostasis.

• Malnutrition: Deficiency of essential nutrients can cause deformities, disease, and death.

Dietary Deficiencies

• Insufficient amino acids is the most common malnutrition.

• Genetic defects disrupting food uptake provide nutrition information (e.g., hemochromatosis).

• Epidemiology studies human health and disease in populations.

• Neural tube defects result from folic acid deficiency.

Food Processing

• Four stages:

  • Mechanical digestion

  • Chemical digestion (enzymatic hydrolysis)

  • Absorption

  • Elimination

• Ingestion: Eating or feeding.

• Digestion: Breaking food down.

• Absorption: Uptake of nutrients.

• Elimination: Passage of undigested material.

Digestive Compartments

• Specialized compartments reduce the risk of self-digestion.

• Gastrovascular cavity functions in both digestion and distribution of nutrients.

• Intracellular digestion: food particles engulfed by phagocytosis.

• Extracellular digestion: breakdown of food particles outside of cells.

Mammalian Digestive System

• Alimentary canal and accessory glands (salivary glands, pancreas, liver, and gallbladder).

• Food is pushed along by peristalsis; sphincters regulate movement.

The Oral Cavity, Pharynx, and Esophagus

• Mechanical digestion occurs in the oral cavity.

• Saliva contains salivary amylase and mucus.

• Tongue shapes food into bolus and pushes it to pharynx, leading to esophagus.

• Epiglottis covers trachea.

Digestion in the Stomach

• Stomach stores food and secretes gastric juice, forming chyme.

• Gastric juice has a pH of about 2 (kills bacteria, denatures proteins) and contains HCl and pepsin.

• Mucus protects the stomach lining.

• Sphincters regulate chyme entry into the small intestine.

• Gastric ulcers are caused by Helicobacter pylori.

Digestion in the Small Intestine

• Chyme mixes with digestive juices from the pancreas, liver, gallbladder, and intestinal wall.

• Pancreas produces trypsin and chymotrypsin and bicarbonate ions.

• Liver produces bile, stored in gallbladder, aids in fat digestion.

Digestion in the Small Intestine

• Epithelial lining produces digestive enzymes.

• Peristalsis moves chyme and juices along the small intestine.

• Most digestion occurs in the duodenum; jejunum and ileum function mainly in absorption.

• Small intestine has villi and microvilli to increase surface area.

• Transport across epithelial cells can be passive or active.

Absorption in the Small Intestine

• Epithelial cells absorb fatty acids and monoglycerides, recombine them into triglycerides, forming chylomicrons.

• Lymphatic vessels deliver chylomicron-containing lymph to veins.

• Hepatic portal vein carries nutrient-rich blood to the liver.

• Liver regulates nutrient distribution and detoxifies molecules.

Absorption in the Large Intestine

• Colon recovers water, houses bacteria that produce vitamins.

• Feces are stored in rectum until elimination.

• Cecum aids in fermentation of plant material; appendix plays a minor role in immunity.

Adaptations of Digestive Systems Correlate with Diet

• Mammals have specialized teeth for different diets.

• Carnivores have large, expandable stomachs; herbivores and omnivores have longer alimentary canals.

Regulation of Digestion, Energy Allocation, and Appetite

• Bioenergetics determine nutritional needs.

• Metabolic rate is energy use per unit of time.

• BMR is minimum metabolic rate of a nongrowing endotherm at rest.

• SMR is the fasting, nonstressed ectotherm rate at a temperature.

• Endothermy is more energetically costly than ectothermy.

Glucose Homeostasis

• Insulin and glucagon maintain glucose levels.

• Insulin levels rise, liver synthesizes glycogen.

• Glucagon stimulates liver to break down glycogen.

• Diabetes mellitus is caused by insulin deficiency or decreased response.

Regulation of Appetite and Consumption

• Overnourishment causes obesity.

• Hormones regulate body weight (ghrelin, insulin, PYY, leptin).

Nutrients Exchange and Transport in Organism

• Animal cells require nutrients and $O_2$ that cross the plasma membrane.

• Multicellular organisms rely on systems that carry out exchange and transport.

• Gills are specialized exchange systems.

• Gastrovascular cavities function in both digestion and distribution of substances (cnidarians, flatworms).

Circulatory Systems

• Circulatory system: circulatory fluid, interconnecting vessels, and a heart.

• Open circulatory system: hemolymph bathes organs directly (insects, arthropods, mollusks).

• Closed circulatory systems: blood is confined to vessels (annelids, cephalopods, vertebrates).

Organization of Vertebrate Circulatory Systems

• Arteries carry blood away from heart to capillaries.

• Venules return blood from capillaries to heart.

• Vertebrate hearts contain atria and ventricle.

Organization of Vertebrate Circulatory Systems

• Bony fishes, rays, and sharks have single circulation with a two-chambered heart.

• Amphibians, reptiles, birds, and mammals have double circulation.

Evolutionary Variation in Double Circulation

• Frogs have a three-chambered heart.

• Turtles, snakes, and lizards also have a three-chambered heart.

• Mammals and birds have a four-chambered heart.

Mammalian Circulation

• Blood flows from right ventricle to lungs, then to left atrium, then to body tissues via aorta.

• Diffusion of $O2$ and $CO2$ takes place in capillary beds.

• Blood returns to heart via vena cava.

The Mammalian Heart

• Cardiac cycle: pumping and filling of blood.

• Atria are thin-walled; ventricles are muscular.

• Cardiac output: volume of blood each ventricle pumps per minute.

• Atrioventricular (AV) valves separate atria and ventricles; semilunar valves control blood flow.

• Heart sounds are caused by recoil of blood against the valves.

Maintaining the Heart's Rhythmic Beat

• Cardiac muscle cells are autorhythmic.

• Sinoatrial (SA) node (pacemaker) sets the rate.

• Impulses travel to the atrioventricular (AV) node then to Purkinje fibers.

• Sympathetic division speeds up; parasympathetic slows down.

Blood Vessel Structure and Function

• Capillaries have thin walls for exchange.

• Arteries have thicker walls than veins.

• Velocity of blood flow is slowest in capillary beds.

Blood Pressure

• Systole is the contraction phase; diastole is the relaxation phase.

• Blood pressure is determined by cardiac output and resistance due to vasoconstriction and vasodilation.

• Nitric oxide induces vasodilation; endothelin induces vasoconstriction.

• One-way valves prevent backflow of blood; blood returns to heart through contraction of smooth muscle and skeletal muscles.

Fluid Return by the Lymphatic System

• Lymphatic system returns fluid (lymph) that leaks from capillary beds to veins.

• Lymph has a similar composition to interstitial fluid.

Blood Composition and Function

• Blood plasma is about 90% water and contains electrolytes.

• Plasma proteins influence blood pH, osmotic pressure, and viscosity.

• Red blood cells contain hemoglobin for $O_2$ transport. Mammals lack nuclei.

• Erythrocytes circulate for 120 days.

• Stem cells produce red blood cells and platelets.

• Leukocytes function in defense.

• Platelets function in blood clotting.

Blood Clotting

• Coagulation: formation of a solid clot from liquid blood.

• Fibrinogen is converted to fibrin.

• Thrombus can block blood flow.

Cardiovascular Disease

• LDL delivers cholesterol to cells; HDL scavenges excess cholesterol.

• Atherosclerosis is caused by plaque buildup in arteries.

• Heart attack is death of cardiac muscle tissue from blockage.

• Stroke is death of nervous tissue in the brain.

Gas Exchange

• Gas exchange is uptake of $O2$ and discharge of $CO2$.

• Partial pressure is pressure exerted by a gas in a mixture.

• A gas undergoes net diffusion from higher to lower partial pressure.

Respiratory Media

• $O2$ is plentiful in air; obtaining $O2$ from water requires greater energy.

Respiratory Surfaces

• Respiratory surfaces tend to be large, thin, and moist.

• Gills are outfoldings of the body.

• Ventilation is the movement of the respiratory medium.

• Fish gills use a countercurrent exchange system.

Respiratory Surfaces

• Tracheal system of insects consists of air tubes.

• Larger insects ventilate their tracheal system.

Respiratory Surfaces

• Lungs are infoldings of the body surface.

• Air passes through pharynx, larynx, trachea, bronchi, and bronchioles to alveoli.

• Cilia and mucus clean the respiratory tract.

Respiratory Surfaces

• Gas exchange takes place in alveoli.

• Alveoli lack cilia and are lined with surfactants.

Breathing Ventilates the Lungs

• Breathing is the alternate inhalation and exhalation of air.

• Amphibians use positive pressure breathing.

• Birds have air sacs that keep air flowing through the lungs.

• Mammals use negative pressure breathing.

Control of Breathing in Humans

• Medulla regulates the rate and depth of breathing.

• Sensors monitor $O2$ and $CO2$ concentrations in the blood.

Respiratory Pigments

• Respiratory pigments increase oxygen transport and mainly consist of metals bound to a protein.

• Hemoglobin is respiratory pigment of vertebrates and many invertebrates.

• Hemoglobin also assists in preventing harmful changes in blood pH.

Respiratory Pigments

• $CO2$ lowers blood pH and decreases affinity of hemoglobin for $O2$ (Bohr shift).

Respiratory Adaptations of Diving Mammals

• Diving mammals have evolutionary adaptations that allow them to perform extraordinary feats. Weddell seals in Antarctica can remain underwater for 20 minutes to an hour, and elephant seals can dive to 1,500 m and remain underwater for 2 hours. These animals have a high blood to body