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chapters 43 & 44 (Osmoregulation and Excretion (44.1 Osmoregulation…
chapters 43 & 44
Osmoregulation and Excretion
44.1 Osmoregulation balances the uptake and loss of water and solutes
osmosis and osmolarity
water enter and leaves cells by osmosis which occurs when two solutions separated by a membrane differ in total solute concentration
two solutions with the same osmolarity are said to be isoosmotic
osmoregularatory challenges and mechanisms
an animal can maintain water balance in two ways. one is to be an odmoconformer to be isoosmotic with its surroundings
the second way to maintain water balance is to be an osmoregulator to control internal osmoralrity independent of that of the external environment
in a hypoosomtic enviroment an osmoregulator must discharge excess water
whether osmoconformers or osmoregulators most animals cannot tolerate substantial change in external osmolarity and are said to be stemohaline
marine animals
most marine invertabrates are osmoconformers
two osmoregulatory strategies evolved among marine vertebrates that address the challenges of a stringly dehydrating environment
cod and other marine bony fishes constantly lose water by osmosis
osmoregulation is frequently coupled to elimination or nitrogenous waste products such as urea
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freshwater animals
the osmoregulatory problems of freshwater animals are the opposite of those of marine animals
salmon and other euryhaline fishes that migrate between fresh water and seawater undergo dramatic changes in osmoregulatory status
animals that live in temporary waters
extreme dehydration or desiccation is fatal for most animals
anhydrobiosis requires adaptations that keep cell membranes intact
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land animals
the threat of dehydration is a major regulatory problem for terrestrial plants and animals
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energetics of osmoregulation
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44.2 an animals nitrogenous wastes reflect its phylogeny and habitat
forms of nitrogenous waste
animals excrete nitrogenous wastes as ammonia urea or uric acid
ammonia
animals that excrete ammonia need access to lots of water because ammonia can be tolerated only at very low concentrations
urea
although ammonia exceretion works well in many aquatic species it is much less suitable for land animals
the main advantage of urea for nitrogenous waste excretion is its very low toxicity
uric acid
insects land snails and many reptiles including birds excrete uric acid as their primary nitrogenous waste
while not primarily uric acid producers humans and some other animals generate a small amount of uric acid from metabolism
the influence of evolution and environment on nitrogenous wastes
as a result of natural selection the type and amount of nitrogenous waste a species produces are matched to its environment
in some cases an animals egg is the immediate environment of relevance to the type of nitrogenous waste excreted
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44.3 diverse excretory systems are variations on a tubular theme
excretory processes
animals across a wide range of species produce a fluid waste called urine through the basic steps (filteration reabsorption secretion and excretion)
the filtrate is converted to a waste fluid by the specific transport of materials into or out of the filtrate
survey of excretory systems
the systems that perform the basic excertory functions vary widely among animal groups
protonephridia
flatworms (phylum platyhelminthes) which lack a coelon or body cavity have excretory systems called protonephridia
during filteration the beating of the cilia draws water and solutes from the intestitial fluid through the flame bulb releasing filtrate into the tubule network
protonephridia are also found in rotifers some annelids mollusc larvae and lancelets
metanephrida
most annelids such as earthworms have metanephridia excretory organs that collect fluid directly from the coelom
earthworms inhabit damp soil and therefore usually experience a net uptake of water by osmosis through their skin
malpighian tubules
insects and other terrestrial arthropods have organs called malpighian tubules that remove nitrogenous wastes and that also function in osmoregulation
as fluid passes from the tubules into the rectum most solutes are pumped back into the hemoltymph water reabsorption by osmosis follows
kidneys
in vertebrates and some other chordates a compact organ called the kidney functions in both osmoregulation and excretion
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44.4 The nephron is organized for stepwise processing of blood filtrate
from blood filtrate to unrine: a closer look
from blood filtrate to urine we'll follow the filtrate along its path in the nephron
proximal tubule
as salt moves from the filtrate to the industrial fluid water follows by osmosis reducing filtrate volume considerably
as the filtrate passes through the proximal tubule materials to be excreted become concentrated
descending limb of the loop of henle
for water to move out of the tubule by osmosis the interstitial fluid bathing the tubule must be hyperosomotic
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solute gradients and water conservation
the ability of the mammalian kidney to conserve water is a key adaptation for terrestrial habitats.
in a mammalian kidney the production of hyperosmotic urine is possible only because considerable energy is expanded for the active transport of solutes against concentration gradients
concentrating urine in the mammalian kidney
to better understand the physiology of the mammalian kidney as a water covering organ lets retrace the flow of filtrate through the excretory tubule
as the filtrate flows from cortex to medulla in the decending limb of the loop of henle water leaves the tubule by osmosis
the loop of henle and surrounding capillaries act as a type of countercurrent system to generate the steep osmotic gradient between the medulla and cortex
what prevents the capillaries of the vasa recta from dissipating the gradient by carrying away the high concentration of NaCl in the medulla's interstitial fluid
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adaptation of the vertebrate kidney to diverse enviroments
vertebrates occupy habitats from rain forests to deserts and from some of the saltiest bodies of water to the nearly pure waters of high mountain lakes
mammals
mammals that excrete the most hyperosmotic urine such as australian hopping mice north american kangaroo rats and other desert mammals have many juxtamendullary nephrons with loops of henle that extend deep into the medulla
44.5 Hormonal circuits link kidney function water balance and blood pressure
homeostatic regulation of the kidney
a combination of nervous and hormonal control manages the osmoregulatory function of the mammalian kidney
antidiuretic hormone
one key hormone in of the kidney is antidiuretic hormone (ADH) also called vasopressin
to undertsand the regulatory circuitry based on ADH lets consider first what occurs when blood osmolarity rises such as after eating salty food or losing water through sweating
The Immune System
43.1: In innate immunity recognition and response rely on traits common to groups of pathogens
Innate Immunity of Invertebrates
the great success of insects in terrestrial and freshwater habitats teeming with diverse pathogens highlights the effectiveness of invertebrate innate immunity
any pathogen that breaches an insect's barrier defenses encounters internal immune diseases
the major immune cells of insects are called hemocytes
the innate immune response of insects is specific for particular classes of pathogens
Innate immunity of vertebrates
in jawed vertebrates innate immune defenses coexist with the more recently evolved system of adaptive immunity
Barrier defenses
the barrier defenses of mammals which block entry of many pathogens include the muccus membranes and skin
beyond their physical role in inhibiting microbial entry body secretions create an environment that is hostile to many pathogens
Cellular innate defenses
in mammals as in insects there are innate immune cells dedicated to detecting devouring and destroying invading pathogens
each TRL protein binds to fragments of molecules characteristic of a set of pathogens
the two main types of phagocytic cells in the mammalian body are neutrophils and macrophages
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antimicrobial peptides and proteins
in mammals pathogen recognition triggers the production and release of a variety of peptides and proteins that attack pathogens or impede their reproduction
interferons are proteins that provide innate defense by interfering with viral infections
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Inflammatory Response
when a splinter lodges under your skin the surrounding area becomes swollen and warm to the touch
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Evasion of innate immunity by pathogens
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43.2 In adaptive immunity receptors provide pathogen specific recognition
antigen recognition by B cells and antibodies
each B cell antigen receptor is a Y-shaped protein consisting of four polypeptide chains: 2 identical heavy chains and 2 identical light chains
each light chain or heavy chain has a constant C region where amino acid sequences vary little among the receptors on different B cells
binding of a B cell antigen receptor to an antigen is an early step in B cell activation, leading to formation of cells that secrete a soluble form of the receptor
the antigen binding site of a membrane bound receptor or antibody has a unique shape that provides a lock and key fit for a particular epitope
B cell antigen receptors and antibodies bind to intact antigen in the blood and lymph
Antigen recognition by T cells
for a T cell the antigen receptor consists of two different polypeptides chains an a chain and a B chain linked by a disulfide bridge
whereas the antigen receptors of B cells bind to epitopes of intact antigens protruding from pathogens or circulating free in body fluids antigen receptors of T cells bind only to fragments of antigens that are displayed or presented in the surface of host cells
The display and recognition of protein antigens begin when a pathogen infects a cell of the animal host or parts of a pathogen are taken in by an immune cell
B cell and T cell development
now that you know how B cells and T cells recognize antigens lets consider four major characteristics of adaptive immunity
receptor diversity and self tolerance arise as a lymphocyte matures
Generation of B cell and T cell diversity
each person makes more than 1 million different B cell antigen receptors and 10 million different T cell antigen receptors
to understand the origin of receptor diversity lets consider an immunoglobulin gene that encodes the light chain of both membrane bound B cell antigen receptors and secreted antibodies
the capacity to generate diversity is built into the structure of Ig genes
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origin of self tolerance
in adaptive immunity how does the body distinguish self from nonself?
proliferation of B cells and T cells
despite the enormous variety of antigen receptor only a tiny fraction are specific for a given epitope
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Immunological memory
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43.3 Adaptive immunity defends against infection of body fluids and body cells
helper T cells: activating adaptive immunity
a type of T cell called a helper T cell activates humoral and cell mediated immune responses
like immune cells infected cells can display antigens on their surface
a helper T cell and the antigen presenting cell displaying its specific epitope have a complex interaction
antigen presenting cells interact with helper T cells in several contexts
B cells and antibodies: A response to extracellular pathogens
secretion of antibodies is the hallmark of the humoral immune response
Activation of B cells
activation of B cells involves both helper T cells and proteins on the surface of pathogens
the pathway for antigen processing and display in B cells differs from that in other antigen presenting cells
B cell activation leads to a robust humoral immune
Antibody function
antibodies do not directly kill pathogens but by binding to antigens they interfere with pathogen activity or mark pathogens in various ways for inactivation or destruction
in opsonization antibodies that are bound to antigens on bacteria do not block infection but instead present a readily recognized structure for macrophages or neutrophilis thereby promoting phagocytosis
when antibodies facilitate phagocytosis as in opsonization they also help fine-tune the humoral immune response
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Cytotoxic T cells: A response to infected host cells
in the absence of an immune response pathogens can reproduce in and kill infected cells
the targeted destruction of an infected host cell by a cytotoxic T cell involves the secretion of proteins that disrupt membrane integrity and trigger cell death
Immunization
the protection provided by a second immune response provides the basis for immunization the use of antigens artificially introduced into the body to generate adaptive immune response and memory cell formation
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Active and Passive Immunity
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43.4 Disruptions in immune system function can elicit or exacerbate disease
exaggerated self directed and diminished immune responses
the highly regulated interplay among hymphocytes other body cells and foreign substances generates an immune response that provides extraordinary protection against many pathogens
allergies
allergies are exaggerated responses to certain antigens called allergens
an acute allergic response sometimes leads to a life threatening reaction called anaohylactic shock
autoimmune diseases
in some people the immune system is active against particular molecules of the body causing an autoimmune disease
heredity gender and environment all influence susceptibility to autoimmune disorders
an additional focus of current research on autoimmune disorders is the activity of regulatory T cells nicknamed tregs
exertion stress and the immune system
many forms of exertion and stress influence immune system function
immunodeficiency disease
a disorder in which an immune system response to antigens is defective or absent is called an immunodeficiency
an inborn immunodeficiency results from a genetic or developmental defect in the production of immune system cells or of specific proteins such as antibodies or the proteins of the complement system
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Evolutionary adaptations of pathogens the underlie immune system avoidance
just as immune systems that ward off pathogens have evolved in animals mechanisms that thwart immune responses have evolved in pathogens
antigenic variation
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