Osmoregulation and Kidneys


Osmoregulation and Kidneys
and Kidneys
Water Balance and Waste Disposal
-Osmoregulation  management of
body’s water content and solute
-MAIN GOAL = maintain
composition of cytoplasm
-Composition of interstitial fluid is
controlled by managing the
comp of blood (ex. Kidneys)
-Transport Epithelia  layers of
epithelial cells that regulate solute
movement; control which direction
and how much solute moves
-Ensures solutes must move
through a semi-permeable
Nitrogenous Waste
-Ammonia  TOXIC!
-Usually converted to a less toxic form
-Animals that secrete ammonia need access to lots of
water (FRESHWATER FISH; it diffuses out into the water)
-Urea  made by mammals, most adult amphibians, marine
fishes and turtles
-Less toxic than ammonia
-Produced by liver  combines ammonia with carbon
-Disadvantage: body uses energy to produce it
-Uric Acid  made by land snails, insects, birds, reptiles
-More expensive to produce than urea (made from
-Urea or Uric Acid….how to decide?
-Mode of Reproduction  reptile/bird eggs = waste
cannot diffuse out; uric acid precipitates out of
solution and can be stored as harmless solid in the
egg until the baby hatches, urea won’t
Osmoregulators vs. Osmoconformers
-Osmoconformer  isoosmotic to
surroundings; marine organisms; water
must have a stable composition
-Osmoregulator  not isoosmotic to
environment, so control internal
osmolarity; enables animals to live in
varied environments (land/ freshwater);
costs energy! (active transport)
-Stenohaline  animals that can’t
tolerate sharp changes in external
osmolarity (both osmoconformers and
-Euryhaline  animals that can tolerate
sharp externals changes in osmolarity
Maintaining water balance in a
MARINE environment
-Maintaining water balance in the sea
-Most marine invertebrates are
- Most marine vertebrates are
-Constantly losing water by
osmosis (water saltier than
internal environments)
-Drink large amounts of seawater
and external salt is secreted by
active transport out of the gills
-Very little urine is produced =
water conservation
Maintaining water balance in a
FRESHWATER environment
-Maintaining water balance in freshwater
-Problem = gain water by osmosis and lose
salt by diffusion
-Contractile vacuoles
-Excrete large amounts of very dilute urine
-Actively uptake salt from surroundings
-Living in temporary water (ex. Puddle)
-Anhydrobiosis  invertebrates lose almost all water
and survive in dormant state when environment dries
up; when water is added, they come back to life
-Maintaining Osmotic Balance on Land
-Adaptations to reduce water loss = waxy cuticle, body
coverings that prevent water loss, nocturnal, eat/drink
moist foods, using metabolic water that is produced in
cellular respiration
Excretory Systems
-2 step process 
-Body fluid (blood,
hemolymph, etc) is
collected (involves
-Usually non-selective
-Selective reabsorption
-Absorb valuable
solutes (glucose, salts,
materials are left in
the filtrate to be
Excretory Systems= Tubular Theme
Do not focus on these….just for reference!
-Protonephridia: Flame bulb system (function in
-Found in flatworms (Platyhelminthes)
-Series of dead end tubules throughout body;
capped by flame bulbs with cilia; cilia wave
water and solutes through (filtration) and
move urine out through the nephridiopores
-Tubules can reabsorb solutes
-Found in annelids; each segment has a pair
-Fluid enters through nephrostome (internal
opening; ciliated funnel) from the coelom;
goes through collecting tubule which includes
a storage bladder and exits to the outside via
the nephridiopore (external opening)
-Has internal openings that collect fluids (storage
-Balance excessive water uptake by making
dilute urine
-Malpighian Tubules
-Found in insects and terrestrial
-Remove nitrogenous waste
-Outfoldings of the digestive
tract; absorb waste from the
hemolymph and empties
into the lumen; water is
reabsorbed and nearly-dry
wasted is excreted
-Vertebrate Kidneys
-Built of tubules and
associated with capillaries
Functional Unit of Kidney= Nephron
-Mammals have a pair of kidneys;
10cm long; supplied with blood by
renal artery and renal vein
-Urine exits each kidney via the ureter
and empties into the urinary
bladder which releases urine via
urethra during urination (which is
controlled by sphincter muscles)
-Structure of a kidney
-Outer part  Renal cortex
-Inner part  Renal medulla
-Both renal cortex and renal
medulla are associated with
many excretory tubules
-Nephron = Functional Unit
-Single long tube
-Ball of capillaries
(glomerulus) surrounded by
Bowman’s capsule
-Filtration of Blood occurs as blood pressure forces fluid from the blood in the glomerulus into
the lumen of Bowman’s capsule
Main Job of
-Pathway of the filtrate:
nephron is carried
-Three regions of the Nephron
out in 4 steps:
(1) Proximal tubule
- Filtration
- Secretion
(2) Loop of Henle (descending/ ascending limbs)
- Reabsorption
- Excretion
(3) Distal Tubule
COLLECTING DUCT = gets emptied into renal pelvis which gets emptied by ureter
capsule has
cells called
which, along
with slit pores
increase the
rate of
Filtration is passive
and nonselective
Secretion is active
and highly
-Cortical Nephrons  shorter loops of Henle; confined to renal cortex; make up
80% of mammalian nephrons
-Juxtamedullary Nephrons  longer loops of Henle that extend into renal
medulla; 20% of mammalian nephrons
Nephrons lined by transport epithelium:
-Afferent arteriole  supplies blood to nephrons; branch of renal artery
-Vasa recta  capillary system that serves the loop of Henle
Reabsorption is
passive, active,
and selective
From Blood Filtrate to Urine
-Proximal Tubule
-Secretion/reabsorption alter
composition of filtrate
-Reabsorb 90% of buffer bicarbonate
-Most important function: reabsorb
water and NaCl
-Transport epithelium
-Very permeable to: water
-NOT very permeable to: salts
and solutes
-Therefore, osmolarity of interstitial
fluid becomes increasingly greater
as it gets towards the inner
medulla (because water flows out
= filtrate becomes more
-Transport epithelium
-Very permeable to: NaCl
-NOT very permeable to: water
-Therefore, loses salt so filtrate
becomes more dilute
-Distal Tube
-Regulates [K+] and [NaCl] of body
fluid by varying amount of K+ that is
-pH regulation
-Important in secretion and
-Collecting duct
-Carries filtrate through medulla to the
renal pelvis
-Water is constantly being absorbed
because the interstitial fluid is more
concentrated, so water diffuses out
 therefore filtrate becomes more
Kidney’s ability to conserve
water = key terrestrial adaptation
-Different permeabilities in the sides of
the loop of Henle maximize
-Most salt is collected in interior of
kidney (inner medulla)
-From the cortex to the inner medulla,
the interstitial fluid increases in
osmolarity; the two solutes that
contribute to this gradient are: NaCl
and Urea
-NaCl diffuses out of the ascending
-Urea diffuses out of the collecting
duct (although most remains in
the duct and is excreted)
-Therefore, there is an osmotic
gradient between the cortex
(low concentration) and medulla
(high concentration)
If the blood pressure falls, the ability of the
nephron to filter blood at Bowman’s capsule
is impaired…so the kidney needs to bring
the BP back up. It does this using 3
Aldosterone  released by the adrenal
glands in response to a drop in BP; tells
distal tubules of the nephron to reabsorb
more sodium ions and water which will
increase the blood volume and pressure
ADH (anti-diuretic hormone; also called
vasopressin)  produced by
hypothalamus but stored in posterior
pituitary; released in response to
dehydration; increases the permeability
of the collecting tubules to water by
opening renal aquaporins… this allows
more water to be reabsorbed (urine
volume reduced)…More on this in a
Renin  released from kidneys; converts
an inactive protein to an active one
called angiotensin, which stimulates the
release of aldosterone from the adrenal
-Kidney uses much
ATP (active
transport of NaCl
out of ascending
loop higher up)
- Juxtamedullary
nephrons (longer
loops) conserve
much water
-Kidney functions are
regulated by:
-Nervous System
-ADH – Antidiuretic Hormone  amplifies water reabsorption
- Also called vasopressin
- Regulates water balance
-Made by the hypothalamus
-Stored and released by pituitary gland
-Osmoreceptor cells in hypothalamus monitor blood
-Low water (ex. Sweating) = increase ADH into blood stream which
gets to kidney; transport epithelium is then made more permeable
to water to reabsorb as much as possible
-Negative Feedback = once levels return to normal, less ADH is
-Also works vice versa if too much water in blood
-Alcohol = inhibits release of ADH; therefore causes excessive water
loss and dehydration
-Adaptations of Vertebrate Kidney
-Long loops of Henle = steep osmotic
gradients in kidneys; concentrated
-Freshwater fish, beavers, etc =
spend much time in fresh water (no
need to conserve water) therefore
they have short loops
-Very important to homeostasis
-Body’s most functionally diverse organ 
-Interacts with circulatory system = takes up
glucose from the blood
-Stores excess glucose as glycogen
-Converts glycogen back to glucose and
releases it in the blood when needed
-Synthesizes plasma proteins (clotting)
-Detoxifies chemical poisons
Types of Muscles
Smooth  involuntary; makes up walls of blood vessels and digestive tract; controlled by autonomic
nervous system
Cardiac  involuntary; striated; makes up the heart; generates its own action potentials (individual
heart cells will beat on their own in a saline solution)
Skeletal  VOLUNTARY; large and multinucleated; work in pairs (one muscle contracts and the other
relaxes – ex. Bicep/tricep)
-Body “design” needs to account for
larger demand for support with
increasing size (elephant skeleton
must be different than a mouse
-Body posture (position of legs
relative to main body) =
important structural feature in
supporting body weight
-Muscles move skeletal parts by
-Muscle contraction = active
-Muscle extension = passive
-Muscles attach to skeletons in
antagonistic pairs so they are
always working against one
another (ex. Biceps and
-Skeletal Muscle (striated)
-Function  attached to bones
and responsible for their
-Structure  consists of a bundle
of long fibers running the length
of the muscle; each fiber is a
single cell with many nuclei
-Each of these fibers are
made up of myofibrils that
are arranged longitudinally
-Myofibrils have two kinds of
-thin filaments – actin
-thick filaments – myosin
- Sarcolemma is a modified PM
that surrounds each muscle
fiber and can propagate an
action potential
Thick filaments
= purple in this
picture 
Thin filaments =
orange in this
picture 
-SARCOMERE – basic
contractile unit of the muscle
-A band = whole length of
thick filaments
-I band = only thin
-Z line = boundaries of the
the sarcomere
-H zone = only the thick
-When the muscle contracts,
the sarcomere gets shorter
because the thick and thin
filaments slide past one
another (degree of overlap
-A bands do not change
in length, I bands shorter,
H zone disappears
Calcium ions and regulatory proteins control muscle contraction
-Muscle at rest = myosin binding sites on actin molecules are blocked by tropomyosin
-Troponin complex = controls position of tropomyosin
-When calcium binds to troponin, it alters the interaction and exposes the myosin
binding sites  actin and myosin can bind and the muscle contracts
SO…when calcium present, muscle can contract
-Calcium concentration regulated by the sarcoplasmic reticulum
Stimulus leading to contraction of
a skeletal muscle at the
Neuromuscular Junction:
motor neuron
 releases a neurotransmitter
 which depolarizes the
postsynaptic muscle cell
 causes and action potential
in the muscle cell
 action potential spreads
deep into the muscle cell (via
the T tubules) to the
sarcoplasmic reticulum
 sarc. ret. releases calcium
 calcium binds to troponin
which alters the interaction
between troponin and
tropomyosin and allows actin
and myosin to bind
 muscle contracts!
Eyes and Vision
Photoreceptors (light detectors) and Vision
-Eye cup  simplest; found in planarians (move away from light); gives info about light intensity and
direction, but no real image
-Compound eyes  forms images; found in insects and crustaceans; made up of thousands of light
detectors called ommatidia which each have their own lens; gives a mosaic image that the brain
can translate into a picture; good at detecting movement
-Single lens eye  found in invertebrates; works like a camera
-Light enters through pupil (small opening); iris changes diameter of pupil; single lens focuses light
onto the retina which consists of light transducing receptor cells
1. Sclera  tough white outer layer of connective
2. Choroid  thin pigmented layer
3. Conjunctiva  mucous membrane that covers
outer surface of the sclera; helps keep the eye moist
4. Cornea  acts as a fixed lens and lets light into the
front of the eye; it’s the front part of the sclera;
conjunctiva does not cover it
5. Iris  gives eye its color; part of the choroids;
regulates amount of light entering the pupil
6. Pupil  hole in center of iris
7. Retina  innermost layer of the eyeball; contains
the photoreceptor cells:
a. Rod cells – more sensitive to light but don’t see
colors; allow us to see at night
b. Cone cells – distinguish colors in the daytime
8. Lens  used for focusing; lens flat = see distant; lens
spherical = see close up
-Can detect more colors than invert eye
-Eye generates action potentials to the vision
centers of the brain which is actually the
part that “sees”
Vertebrate Single
Lens Eye
Photons of light pass through the lens and get focused on the retina. In the retina, we have RODS
(black/white vision) and CONES (color vision). In these cells they have Retinal (light absorbing
pigment), which changes shape when exposed to light and that shape change excites the visual
pigment called Rhodopsin. This triggers the signal transduction pathway and amplification cascade
which uses G proteins.
The stimulation of the retinal activates a G-protein signaling mechanism that ultimately alters the
membrane potential and closes Na+ channels (in the absence of light these channels are open). Each
single molecule of photoexcited rhodopsin activates several hundred enzyme molecules, each of
which activates several hundred molecules of cGMP, closing hundreds of Na+ channels, and causing
an impulse to be sent to the optic nerve. From the optic nerve, impulses travel to the cortex of the
brain where the messages are interpreted and seeing actually occurs.
Sex Differences
Primary Sex Characteristics 
structures that assist in the vital
process of procreation; ex.
Testes, ovaries, uterus
Secondary Sex Characteristics
 notable physical differences
between males and females;
ex. Facial hair, deepness of
voice, breasts, muscle
Males – XY, Females - XX
Male sexual anatomy is designed for the delivery of
sperm to the female reproductive system:
Testes  male gonads; produces sperm in the
seminiferous tubules and hormones in the
interstitial cells
Epididymis  coil that extends from the testes;
sperm complete their maturation here; sperm
gain motility here
Vas Deferens  muscular tube that carries
sperm from the epididymis to the urethra
Urethra  passageway through which sperm
exits during ejaculation; also the tunnel that
urine uses to be excreted
Prostate gland  adds a basic liquid to the
sperm to combat the acidity of the vagina;
secretes the semen directly into the urethra
Seminal Vesicles  adds 3 important things to
the Vas Deferens to send along with the sperm
during ejaculation:
Fructose = sugar for energy
Prostaglandins = hormone that stimulates
uterine contraction
Mucus = helps sperm swim more efficiently
Male Anatomy
Female Anatomy
Ovaries  female gonads; where
meiosis occurs; site of egg
Fallopian Tube  also called the
oviduct; eggs are released from
the ovary (called ovulation) and
go into the fallopian tube; most
fertilization occurs here
Uterus  eggs get delivered here
from the fallopian tube; if the egg
was fertilized by the sperm, the
blastocyst implants in the lining of
the uterus called the
Cervix  opening of the uterus
into the vagina
Vagina  birth canal; sperm
enters the female reproductive
system here
Oogenesis vs. Spermatogenesis
Processes of meiosis to produce gametes
 Spermatogenesis:
 Occurs in testes
 Males do not form gametes until puberty
 Primary spermatocytes do meiosis I to produce two
secondary spermatocytes which undergo meiosis II,
producing four spermatids (immature sperm)
 Oogenesis:
 Occurs in ovaries
 Primary oocytes are made from fetal cells and halt at
prophase I until puberty
 Primary oocyte does meiosis I to form the secondary
oocyte and a polar body
 If the egg gets fertilized, that primary oocyte does
meiosis II and produces an egg (to combine with the
sperm to make the zygote) and another polar body
 Things to remember:
 A primary oocyte could sit in the ovary for 40
years before completing the first stage of meiosis
 The beginning of each menstrual cycle causes a
primary oocyte to resume Meiosis I
 Oocytes only undergo Meiosis II after fertilization
Menstrual Cycle of
Follicular phase  several follicles in the
ovaries grow and secrete increasing
amounts of estrogen in response to folliclestimulating hormone (FSH) from the anterior
Ovulation  the second oocyte ruptures
out of the ovaries in response to the
luteinizing hormone
Luteal Phase  the corpus luteum forms in
response to luteinizing hormone; it is the
follicle left behind after ovulation and
secretes estrogen and progesterone, which
thicken the endometrium of the uterus
Menstruation  monthly shedding of the
lining of the uterus when implantation does
NOT occur
Hormone control of the Menstrual Cycle
Sperm swim through the
cervix and uterus and end
up in the fallopian tube
There they come into
contact with an egg
Enzymes released by
the head of the sperm
(the acrosome)
penetrate the jelly coat
of the egg
Once one sperm
penetrates the egg, the
others are kept out
because of a chemical
change that occurs
The nucleus of the
sperm and the nucleus
of the egg fuse to form
a diploid zygote
Cleavage = divisions
Mitotic divisions begin immediately after
Morula → solid ball of 16 cells not much
larger than the zygote (occurs after 4
This divides and releases a fluid to form a
Blastocyst (or blastula) → hollow ball of cells
with a large, fluid-filled cavity
The blastocyst then reaches the uterus
and burrows into the lining; this is called
Two parts to the blastocyst:
Inner Cell Mass  becomes the
Trophoblast  becomes the
placenta; makes hCG which
maintains the endometrium
Remember: Pregnancy begins at implantation!
Order of Process:
- Starts with fertilization…then
Zygote  Cleavage  Blastula  Gastrula  Organ formation
At each phase the # of cells increases, but the # of chromosomes in each cell stays the
After cleavage, gastrulation
occurs  cells separate into
three germ layers:
Ectoderm → nervous
system (spinal cord,
neurons, brain) and
epidermis (skin, hair, nails)
Mesoderm → muscles,
connective tissue,
skeletal system,
reproductive system,
Endoderm → linings of
digestive, respiratory, and
urinary tracts; glands
(liver, pancreas, thyroid)
Archenteron = simple
digestive cavity
formed during the
formation of the germ
Organogenesis  organ
Nervous System
Derived primarily from the
Notochord  present only
in embryos in vertebrates;
supports the body
Neural Plate  Neural
Groove  Neural Tube…
which gives rise to the
central nervous system!
Somite  gives rise to
muscles and vertebrae in
Extraembryonic Structures
Yolk Sac  site of early blood
cells in humans
Chorion  outer membrane of
the embryo; site of
implantation; contributes to
formation of placenta in
mammals; diffusion of gasses
Allantois  mammalian waste
transporter; becomes the
umbilical cord
Amnion  encloses the embryo
in protective amniotic fluid
provides nutrients and
oxygen to the embryo
and helps dispose of its
metabolic wastes
Nutrients, gases, drugs
pass from mom to baby
through the placenta
by diffusion ; mom’s and
baby’s blood never
Fetus is attached to the
placenta by the
umbilical cord
Factors in Cellular Differentiation
Cytoplasmic Determinants 
Asymmetry contributes to
differentiation, since different
areas have different amounts of
cytoplasm, and thus perhaps
different organelles and
cytoplasmic structures; the
cytoplasm surrounding the
nucleus has profound effects on
the developing embryo
Induction  One group of cells
infulences another group of cells
through physical contact or
chemical signaling
Homeotic Genes  master
regulatory genes; these
determine how segments of an
organism will develop
Induction  the influence on one
group of cells on the development of
another through physical contact or
chemical signaling
Hans Spemann  his experiments
showed that the notochord induces
cells in the dorsal ectoderm to
develop into the neural plate; when
cells from the notochord are
transplanted somewhere else in the
embryo, the neural plate develops
in the new location
Two main systems involved:
1. Endocrine (hormones)
2. Muscular
Birth initiated by hormones of
both the mother and the fetus
Oxytocin → causes the
smooth muscles of the uterus
to contract; secreted by the
pituitary gland
“water breaks” → amniotic sac
Cervix begins to enlarge
Labor → muscular contractions leading
up to the birth
Baby is born; umbilical cord is cut
Afterbirth → placenta, amnion, and the
uterine lining are expelled about 10 min
after childbirth
Baby cries = good signs → breathing on
its own
Respiratory and excretory systems
become functional

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