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10.1 Urinary System
Excretion is the removal of metabolic wastes from the body. The kidneys are the primary organs of excretion.
Organs of the Urinary System
Kidneys
The kidneys are paired organs located near the small of the back, on either side of the vertebral column. The
kidneys produce urine.
Ureters
The ureters conduct urine from the kidneys to the bladder. Peristaltic contractions cause urine to enter the bladder.
Urinary Bladder
The urinary bladder stores urine until it is expelled from the body through the urethra. The bladder wall is
expandable.
Urethra
The urethra is a small tube that extends from the bladder to an external opening. The urethra has a different length
in females than in males. In males, the urethra carries urine during urination and sperm during ejaculation.
Functions of the Urinary System
The functions of the urinary system include: excretion of metabolic wastes, notably nitrogenous wastes; maintenance of
water-salt balance; maintenance of acid-base balance; and secretion of hormones.
10.2 Kidney Structure
Macroscopically, the kidneys are divided into the renal cortex, renal medulla, and renal pelvis. Microscopically, kidneys contain the
nephrons.
Anatomy of a Nephron
Each nephron has its own blood supply; the afferent arteriole approaches the glomerular capsule and divides to become the
glomerulus, a capillary tuft. The permeability of the glomerular capsule allows small molecules to enter the capsule from the
glomerulus. The efferent arteriole leaves the capsule and immediately branches into the peritubular capillary network.
Parts of Nephron
Each region of the nephron is anatomically suited to its task in urine formation. The spaces between podocytes of
the glomerular capsule allow small molecules to enter the capsule from the glomerulus, a capillary knot. The
cuboidal epithelial cells of the proximal convoluted tubule have many mitochondria and microvilli to carry out
active transport (following passive transport) from the tubule to blood. In contrast, the cuboidal epithelial cells of the
distal convoluted tubule have numerous mitochondria but lack microvilli. They carry out active transport from the
blood to the tubule.
10.3 Urine Formation
Glomerular Filtration
During glomerular filtration, small molecules including water, wastes, and nutrients move from the glomerulus to the inside
of the glomerular capsule.
Tubular Reabsorption
During tubular reabsorption, primarily nutrients and water, moves from the proximal convoluted tubule into the blood of the
peritubular capillary network. Only those molecules recognized by carrier molecules are actively reabsorbed. The amount of
a substance that can be reabsorbed is limited by its number of carrier molecules.
Tubular Secretion
During tubular secretion, certain substances like hydrogen ions, creatinine, and penicillin move from the blood into the distal
convoluted tubule.
10.4 Regulatory Functions of the Kidneys
The kidneys maintain the water-salt balance of the blood within normal limits. In this way they also maintain the blood volume and
blood pressure.
Reabsorption of Water
Water is reabsorbed from the loop of the nephron and the collecting duct. This reabsorption of water requires reabsorption of
salt and the establishment of a solute gradient dependent on salt and urea. Hormones regulate the reabsorption of sodium at
the distal convoluted tubule and the reabsorption of water at the collecting duct.
Diuretics
Diuretics are chemicals that increase the flow of urine. Diuretics like alcohol and caffeine have various modes of
action. Diuretic drugs can counteract high blood pressure.
Acid-Base Balance of Body Fluids
The normal pH for body fluids is about 7.4. If the blood pH rises above that, a person is said to have alkalosis. If the blood
pH decreases below that, a person is said to have acidosis. These are abnormal conditions that need medical attention.
Acid-Base Buffer Systems
The pH of the blood stays near 7.4 because the blood is buffered. One of the most important buffers in the blood is
a combination of carbonic acid and bicarbonate ions.
Respiratory Center
The respiratory center in the medulla oblongata increases the breathing rate if the hydrogen ion concentration of the
blood rises.
The Kidneys
Only the kidneys can rid the body of a wide range of acid and basic substances. The kidneys are slower acting than
the buffer systems and respiratory center, but they have a more powerful effect on pH.
10.5 Disorders with Kidney Function
Damage, especially recurring urinary infections, can lead to glomeruli that allow large molecules like proteins to be in the filtrate or
glomeruli that simply do not function any more.
Hemodialysis
The usual form of hemodialysis involves cleansing the patient’s blood by passing it through dialysis tubing in contact with a
dialysis solution. Wastes and excess salts pass out of the tubing into the dialysis solution. In continuous ambulatory
peritoneal dialysis (CAPD), the dialysis solution is introduced into the peritoneal cavity. Wastes filter from the blood into the
solution which is removed 4 to 8 hours later.
Replacing a Kidney
When kidneys fail, kidney transplants can be successful, especially if the donor is a close relative.
10.6 Homeostasis
The urinary system works with the other body systems to maintain homeostasis.
The Kidneys Excrete Waste Molecules
The kidneys remove metabolic waste which is absolutely necessary for maintaining homeostasis.
Water-Salt Balance
The kidneys regulate the water-salt balance which affects blood volume and blood pressure.
Acid-Base Balance of Blood
Only the kidneys can rid the body of a wide range of acidic and basic substances, so the kidneys have ultimate control over
blood pH.
The Kidneys Assist Other Systems
The kidneys produce renin and assist the endocrine and cardiovascular systems.
EXTENDED LECTURE OUTLINE
11.1 Overview of Skeletal System
The skeleton system consists of 206 bones (in adults) along with the cartilage and ligaments that occur at the joints.
Functions of the Skeleton
The skeleton supports the body, protects soft body parts, produces blood cells, stores minerals and fat, and permits flexible
body movement along with the muscles.
Anatomy of a Long Bone
The shaft of a bone is called the diaphysis. It has a large medullary cavity whose walls are composed of compact bone. The
expanded region at the end of a long bone is called an epiphysis. The epiphyses are composed largely of spongy bone that
contains red bone marrow. A long bone is covered by the periosteum except for the articular cartilage on its ends.
Bone
Compact bone is made up of osteons, lacunae in concentric circles around a central canal. Canaliculi run through the
matrix of bone, connecting lacunae and central canals. Spongy bone contains plates called trabeculae, the spaces of
which are filled with red bone marrow for blood cell production. Bone cells are osteocytes.
Cartilage
Cartilage is weaker and more flexible than bone, and is slower to heal because of its lack of direct blood supply.
Hyaline cartilage has a matrix made of collagen and is found at the ends of long bones and in the nose and trachea.
Stronger fibrocartilage has thick rows of collagen fibers and is able to tolerate pressure and tension. Flexible elastic
cartilage contains mostly elastin fibers and is found in the external ear and epiglottis.
Fibrous Connective Tissue
Fibrous connective tissue contains fibroblasts with collagenous fibers and makes up the ligaments that attach bone to
bone and muscle to bone at joints.
11.2 Bone Growth, Remodeling, and Repair
Three different cell types are involved in bone growth and repair. Osteoblasts are bone-forming cells. Osteocytes are mature bone cells
arising from osteoblasts. Osteoclasts resorb bone.
Bone Development and Growth
Ossification refers to the formation of bone.
Intramembranous Ossification
Intramembranous ossification occurs between flat sheets of connective tissue. Osteoblasts lay down bone, forming
trabeculae. Compact bone is then laid down over the outside surfaces. Skull bones form this way.
Endochondral Ossification
Most bones form by endochondral ossification, with a cartilage model filled in with bone. Osteoblasts fill in areas of
the center of the cartilage model that have begun to break down. Compact bone is also laid down under the
periosteum. The epiphyses of long bones continue to grow from a growth plate.
Final Size of the Bones
When the epiphyseal plates close, bones can no longer increase in length.
Hormones Affect Bone Growth
Vitamin D and growth hormone (GH) affect the growth of the bones.
Bone Remodeling and Its Role in Homeostasis
In adults, the actions of osteoclasts and osteoblasts continually remodel bones. Bone recycling allows the body to regulate
the amount of calcium in the blood. Bone remodeling also accounts for why bones can respond to stress.
Bone Repair
About 6 to 8 hours after a fracture, a hematoma (large blood clot) forms at the fracture site. A fibrocartilage callus fills in the
break. A bony callus formed by osteoblasts replaces the cartilage and lasts for four months. Osteoclasts eventually remodel
the bone, building a new medullary cavity. Fractures are named according to the type of break (e.g., spiral).
Vertebral Fusion
During fusion surgery, bone grafts are placed around the spine. The body joins the grafts to the vertebrae fusing the
vertebrae together.
11.3 Bones of the Axial Skeleton
The axial skeleton lies in the midline of the body and consists of the skull, hyoid bone, vertebral column, ribs, and sternum.
The Skull
The skull is formed by the cranium and the facial bones.
The Cranium
The cranium is made up of eight bones that are incompletely fused in infants, leaving soft spots, or
fontanels. Sinuses are found in the cranium. They reduce the weight of the skull and give
resonance to the voice. The major bones of the cranium include the frontal bone, two parietal
bones, an occipital bone housing the foramen magnum, two temporal bones, a sphenoid bone, and
an ethmoid bone. The sphenoid bone makes up the floor of the cranium. The ethmoid bone helps
form the orbits and the nasal septum.
The Facial Bones
The frontal bone of the skull forms the forehead of the face. The lower jaw is made up of the
mandible. Zygomatic bones make up the cheekbones, and maxillae form the upper jaw. Two nasal
bones form the bridge of the nose.
The Hyoid Bone
The hyoid bone is located superior to the larynx, anchors the tongue, and serves as a point of attachment for
muscles used in swallowing.
The Vertebral Column
The vertebral column supports the head and trunk, protects the spinal cord and nerves, and is a site for
muscle attachments. Each vertebra has facets that articulate with each other and spinous processes that
project toward the back.
Types of Vertebrae
Cervical vertebrae are in the neck region and include the atlas and axis. Thoracic vertebrae are in
the upper back and have an extra facet for rib attachment. Thick lumbar vertebrae are in the lower
back. Five sacral vertebrae fuse to form a sacrum. The coccyx, or tailbone, is at the base of the
vertebral column.
Intervertebral Disks
Intervertebral disks, formed of fibrocartilage, provide padding between vertebrae.
The Rib Cage
The rib cage is composed of the thoracic vertebrae, the ribs and their cartilages, and the sternum.
The Ribs
The 12 pairs of ribs all connect to the thoracic vertebrae. The upper seven pairs of ribs connect to the
sternum via costal cartilage. The lower two pairs of ribs are “floating ribs” because they are not attached to
the sternum.
The Sternum
The sternum (breastbone) protects the heart and lungs. It is made of the manubrium, the body, and the
xiphoid process.
11.4 Bones of the Appendicular Skeleton
The appendicular skeleton is made up of the pectoral and pelvic girdles, and the arm and leg bones.
The Pectoral Girdle and Upper Limb
The pectoral girdle consists of the scapula (shoulder blade), and the clavicle (collarbone). The glenoid cavity
articulates with the head of the humerus. The humerus is the bone of the upper arm. The radius and ulna make up the
lower arm. The hand is made up of eight carpal bones, with five metacarpals and the phalanges of the fingers and
thumb.
The Pelvic Girdle and Lower Limb
The pelvic girdle consists of two heavy coxal bones, fused at the sacrum. Each coxal bone is made up of the ilium,
ischium, and pubis, all fused at the acetabulum. The male pelvis and the female pelvis differ somewhat due to
different functions. The female pelvis is more flared. The thigh contains the femur, and the lower leg is made up of
the tibia and fibula. The ankle contains seven tarsal bones, and five metatarsals make up the arching instep of the
foot.
11.5 Articulations
Bones are joined at the joints, which are classified as fibrous, cartilaginous, or synovial. Fibrous joints are immovable. Cartilaginous
joints are connected by hyaline cartilage and tend to be slightly movable. Synovial joints are freely movable.
Movements Permitted by Synovial Joints
Synovial joint movements include flexion, extension, abduction, rotation, circumduction, inversion and eversion.
EXTENDED LECTURE OUTLINE
12.1 Overview of Muscular System
All muscles contract or shorten.
Types of Muscles
Smooth muscle fibers are spindle-shaped cells, each with a single nucleus. Contraction of smooth muscle is involuntary.
Cardiac muscle forms the heart wall. Its fibers are generally uninucleated, striated, tubular, and branched. Cardiac fibers
relax completely between contractions, which prevents fatigue. Skeletal muscles fibers are tubular, multinucleated, and
striated. Skeletal muscle contraction is voluntary.
Functions of Skeletal Muscles
Skeletal muscles support the body, make bones move, help maintain a constant body temperature, assist movement in
cardiovascular and lymphatic vessels and help protect internal organs and stabilize joints.
Skeletal Muscles of the Body
Skeletal muscles are attached to the skeleton, and their contraction causes the movement of bones at a joint.
Basic Structure of Skeletal Muscles
A whole muscle contains bundles of skeletal muscle fibers called fascicles. Within a fascicle, each fiber is
surrounded by connective tissue, and the fascicle itself is also surrounded by connective tissue. Muscles are covered
with fascia, a type of connective tissue that extends beyond the muscle and becomes its tendon, anchoring the
muscle to the bone.
Skeletal Muscles Work in Pairs
The origin of a muscle is the end attaching to the immovable bone; the insertion of a muscle is the end attaching to
the movable bone. Muscles are frequently grouped as synergists and antagonists.
Names and Actions of Skeletal Muscles
Skeletal muscles are named according to their size, shape, location, direction of fibers, attachment, number of attachments, or
action.
12.2 Skeletal Muscle Fiber Contraction
Muscle Fibers and How They Slide
The plasma membrane of a muscle fiber is its sarcolemma. Its endoplasmic reticulum is called the sarcoplasmic reticulum,
which stores calcium. The sarcolemma invaginates into T tubules that contact the sarcoplasmic reticulum. Within muscle
fibers are the contractile myofibrils.
Myofibrils and Sarcomeres
Myofibrils are cylindrical structures within muscle fibers. Myofilaments that make up myofibrils are arranged such
that they exhibit striations. Striations are grouped into contractile units called sarcomeres. Within sarcomeres, thick
filaments are made up of myosin, and thin filaments are made up of actin.
Myofilaments
Thick Filaments
A thick filament is composed of several hundred molecules of the protein myosin which is shaped like a
golf club, with a straight portion ending in a globular head or cross-bridge.
Thin Filaments
A thin filament consists of two intertwining strands of the protein actin.
Sliding Filaments
When a nervous impulse reaches a muscle fiber, the sarcoplasmic reticulum releases its stored calcium, and
the fiber contracts. The myosin filaments have cross-bridges that pull on the actin myofilaments, causing
them to slide past each other. The sliding filament theory states that the filaments do not change in length
as the sarcomere shortens.
Control of Muscle Fiber Contraction
The region where a motor neuron contacts a muscle fiber is called the neuromuscular junction. A motor nerve fiber expands
into a synaptic end bulb as it approaches a muscle fiber. When a nerve impulse travels down the neuron, synaptic vesicles
storing a neurotransmitter acetylcholine (ACh) move to the end of the bulb, releasing the ACh into the synaptic cleft. The
muscle fiber receives the neurotransmitter at receptor sites. The sarcolemma generates impulses that travel over the
sarcolemma to the T tubules and sarcoplasmic reticulum. Stored calcium is released to the cell, triggering contraction.
Threads of tropomyosin wind about an actin filament, and troponin occurs at intervals along the threads. When calcium ions
are released from the sarcoplasmic reticulum, they combine with troponin, and this causes tropomyosin threads to shift their
position, exposing the myosin binding sites. The myosin can now bind to the actin.
12.3 Whole Muscle Contraction
Muscles Have Motor Units
A nerve fiber, together with all of the muscle fibers it innervates, is called a motor unit. A motor unit obeys the all-or-none
law. When a motor unit is stimulated by infrequent electrical impulses, a single contraction occurs that lasts only a fraction
of a second. This response is called a muscle twitch. If a motor unit is given a rapid series of stimuli, it can respond to the
next stimulus without relaxing completely. Summation is increased muscle contraction until maximal sustain contraction,
called tetanus, is achieved.
Muscle Tone
When some motor units are always contracted but not enough to cause movement, the muscle is firm and solid. It
has good tone.
Energy for Muscle Contraction
Fuel Sources for Exercise
A muscle has four possible energy sources. Two of these are stored in muscle: glycogen and fat. Two of these are
acquired from blood: blood glucose and plasma fatty acids.
Sources of ATP for Muscle Contraction
Muscle cells store limited amounts of ATP but can acquire more ATP once stored ATP has been used up.
The CP Pathway
The simplest and fastest way for muscles to produce ATP is to use the CP pathway. Creatine phosphate is
converted to creatine with the conversion of ADP to ATP.
Fermentation
Fermentation produces two ATP from the breakdown of glucose to lactate anaerobically. This pathway
most likely begins with glycogen. Formation of lactate is noticeable because it produces muscle aches and
fatigue upon exercising.
Cellular Respiration
Cellular respiration is more likely to supply ATP when exercise is submaximal in intensity. It can make
use of glucose from the breakdown of glycogen stored in muscle, glucose taken up from blood, and fatty
acids.
Fast-Twitch and Slow-Twitch Muscles Fibers
Fast-twitch fibers tend to rely on CP and fermentation while slow-twitch fibers tend to prefer cellular respiration.
Fast-Twitch Fibers
Fast-twitch fibers tend to be anaerobic and seem to be designed for strength because their motor units contain many
fibers. They are light in color because they have fewer mitochondria, little or no myoglobin, and fewer blood
vessels than slow-twitch fibers.
Slow-Twitch Fibers
Slow-twitch fibers have a steadier tug and have more endurance despite more units with smaller numbers of fibers.
These produce most of their energy aerobically. They have many mitochondria and are dark in color because they
contain myoglobin.
Delayed Onset Muscle Soreness
Delayed onset muscle soreness generally appears some 24–48 hours after strenuous exercise. It is thought that this is due to
tissue injury that takes several days to heal. To prevent this, try warming up thoroughly and cooling down completely.
Stretch after exercising.
12.4 Muscular Disorders
Common Muscular Conditions
Spasms are involuntary muscle contractions that may cause pain. Cramps are long, painful spasms. A strain is an
overstretching of a muscle; a sprain is a twisting of a joint leading to swelling and injury, not only of muscles but also of
ligaments, tendons, blood vessels, and nerves.
Tendonitis and Bursitis
In tendonitis, the normal gliding motion of a tendon is impaired, the tendon is inflamed, and movement of a joint
becomes painful. The most common cause of tendonitis is overuse. A bursa provides a smooth, slippery surface
where muscles and tendons glide over bones. Bursitis is an inflammation of a bursa. Bursitis usually results from a
repetitive movement or from prolonged and excessive pressure.
Muscular Diseases
Myalgia and Fibromyalgia
Myalgia refers to achy muscles. Fibromyalgia is a chronic condition whose symptoms include achy pain, and
tenderness and stiffness of muscles.
Muscular Dystrophy
Muscular dystrophy is a broad term applied to a group of disorders that are characterized by a progressive
degeneration and weakening of muscles.
Myasthenia Gravis
Myasthenia gravis is an autoimmune disease characterized by muscle weakness. The immune system mistakenly
produces antibodies that destroy acetylcholine receptors.
Amyotrophic Lateral Sclerosis
Amyotrophic lateral sclerosis is better known as Lou Gehrig’s disease. ALS sufferers experience gradual loss of
ability to walk, talk, chew, and swallow.
12.5 Homeostasis
This section concentrates on the contribution of both the muscular and skeletal systems to homeostasis.
Both Systems Produce Movement
The skeletal and muscular systems work together to enable body movement.
Both Systems Protect Body Parts
The skeletal system plays an important role just by protecting the soft internal organs of your body. The muscular system
pads bones.
Bones Store and Release Calcium
Under the direction of the endocrine system, the skeletal system performs tasks that are vital for calcium homeostasis.
Blood Cells are Produced in Bones
Red bone marrow is the site of blood cell production.
Muscles Help Maintain Body Temperature
The muscular system contributes to body temperature.