Urinary system

Announcements
- Urinary system
- Lab Practical Week after Spring Break
- Practical Review this Sunday 23rd at 3-5 pm

Functions of Urinary System
- Kidneys carry out four functions:
(a) Filter nitrogenous wastes, toxins, ions, etc. from blood to be excreted as urine.
(b) Regulate volume and chemical composition of blood (water, salts, acids, bases).
(c) Produce regulatory enzymes.
(d) Renin – regulates BP/ kidney function                                                           (e) Erthropoeitin – stimulates RBC production from marrow.
(f) Metabolism of Vitamin D to active form.

Urinary System

(a) Two Kidneys
- Perform all functions except actual excretion.

(b) Two Ureters
- Convey urine from Kidneys to Urinary Bladder

(c) Urinary Bladder
- Holds Urine until excretion

(d) Urethra
-  Conveys urine from bladder to outside of body

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Kidney general info
- Lie against posterior abdominal wall at level of T12-L3.
- Right kidney is lower than left kidney due to the shape of the liver.
- Lateral surface of kidney is convex while medial is concave : (a) Concave side has a cleft - Renal Hilus  (b) Inside hilus is Renal sinus - Where kidneys receive renal vessels and nerves.

Kidney External Anatomy
- Average size – 12cm x 6cm x 3 cm
- Weights 150 grams or 5 oz
- Surrounded by three membranes (deep to superficial) : (a) Renal capsule – fibrous barrier for kidneys (b) Adipose capsule – fatty tissue designed for protection / stability (c) Renal fascia – dense fibrous CTP anchors kidneys/ adrenals/ membrane 1 and 2 to surroundings.

Kidney Anatomy
- Renal arteries and veins
- Renal cortex
- Renal medulla
- Nephron
- Renal pyramids (6-10)
- Renal papilla
- Calyx (ces)
- Renal pelvis
- Ureter

Nephron
- Blood processing unit which serves to produce urine
- 1 million per kidney
- Consists of a glomerulus and tubules

Urinary system : Kidney and Nephron

Urine Formation III

Countercurrent Multiplication in the Nephron Loop:

(a) Descending limb
- Goes into medulla  - increasing salt gradient
- Water leaves
- Fluid concentrates

(b) Ascending limb
- Goes up toward cortex - decreasing salt gradient
- Na+ pumped out
- Fluid relatively diluted

Urine Formation IV
- Collecting duct
- Travels down into medulla
- Water leaves tubule and enters blood
- Urine becomes concentrated and enters renal papilla
- ADH controls water channel
- ADH – Antidiuretic hormone

Urine Formation : Micturition

(a) Ureters

- 25 cm long

- Enters on the floor of bladder

(b) Urinary Bladder

- Muscular sac on floor of pelvic cavity

- Muscle layer formed by detrusor muscle

- Average bladder volume is 500 ml

- Max capacity is 700-800 ml

(c) Urethra

- Conveys urine out of body

- Female urethra – 3 - 4 cm

- Opens into external urethral oriface

- Lies between vaginal oriface and clitoris

- Male urethra – 18 cm

- 3 regions:
(i) Prostatic urethra – 2.5 cm
(ii) Membranous urethra – 0.5 cm
(ii) Penile urethra – 15 cm

Kidney stones

- A hard granule of calcium, phosphate, uric acid and protein.

- Form in renal pelvis and get lodged in pelvis or ureter.

- Caused by urinary tract infections, dehydration, pH imbalances, or an enlarged prostate gland.

- Treated with stone dissolving drugs, surgical removal, or lithotripsy (ultrasonic vibrations).

Cardiovascular

Cardiac Cycle and Heart Sounds

• Cardiac Cycle refers to one complete heartbeat.
• The heart is actually 2 pumps situated side by side, so a complete cycle consists of contractions of both atria and both ventricles.
• The average resting heart rate is approximately 75 beats per minute
• Resting heart rate will vary with degree of physical conditioning as well as with disease states
• The familiar “lub-dub” associated with the function of the heart are known as heart sounds.
• The heart sounds are made by the heart valves snapping closed under contractile pressure.       

Heart Sounds and Cardiac Output

• The “lub” is caused by the closure of the AV valves
• The “dub” is caused by the closure of the semi-lunar valve.
• Cardiac output (CO) is the amount of blood pumped out of each side of the heart      ( meaning the ventricles ) in one minute
• The value of CO is calculated as the product of the Heart Rate ( HR) multiplied by the Stroke Volume (SV)
• SV generally increases as the force of the ventricular contractions increases.
• CO = HR  x SV
• CO = 75 beats per min x 70mls per beat
• CO = 5250 ml/min
• Generally speaking, blood starting in the heart should complete a circuit of the body and arrive back in the heart in one minute.
• According to Starling’s Law of the heart, stroke volume is influenced by the amount of stretching force applied to the muscle cells of the heart.
• The more the cells are stretched, the great the contraction will be

Starling’s Law of the Heart

• A healthy, efficient heart only pumps about 60% of the volume of blood in the ventricles.
• Venous return is critical to the amount of stretching the heart undergoes.
• If one side of the heart begins to pump more blood than the other, the increase in venous return to the opposite ventricle will force it to pump a larger volume of blood.
• This helps prevent back ups and increased pressures in the system.
• Anything that increases the volume or speed of venous return will also increase the SV and CO.
• The squeezing actions of skeletal muscles on veins also plays a major role in increasing venous return.

Regulation of Heart Rate

• Coronary contraction does not depend on stimulus from the nervous system, because the heart has it’s own intrinsic pacemakers ( SA and AV nodes)
• HOWEVER—heart rate can be temporarily influenced by stimulus from the autonomic nerves.

• Sympathetic nerves can act to increase or decrease the heart by stimulating the SA or AV nodes.
• Parasympathetic nerves act to decrease the heart rate
• Being excited or startled can cause a rapid increase in heart rate.
• Heart rate can also be influenced by hormones
• Epinephrine and Thyroxine mimic the effects of the sympathetic nerves.
• Ion concentrations also has a rofound influence on the heart.
• Decreased Ca+ will depress the heart rate
• Excessive Ca+ will cause prolonged contractions, and possibly stop the heart from beating. 

CHF and Blood Vessels

• When the pumping efficiency of the heart is depressed so that circulation is inadequate to meet tissues needs, congestive heart failure (CHF) results.
• CHF is usually a progressive condition, and in most cases reflects diminished coronary circulation by coronary atherosclerosis
• Each side of the heart can fail independently
• If the left side fails, pulmonary congestion will occur.
• The right side continues to pump blood, but the left side is unable to push oxygenated blood into systemic circulation
• The blood vessels of the lungs become swollen with blood, and the increased pressure forces fluids to leak from circulation and into the lung tissue, resulting in pulmonary edema.
• Suffocation will result if this condition is untreated.
• If the right heart fails, blood is not moved out of the systemic circulation, and peripheral congestion will occur.
• This results in edema in distal parts of the body, such as the feet, ankles and hands.
• Failure of one side of the heart places increased strain on the opposite side of the heart—eventually leading to whole heart failure

Blood Vessels 

• Blood circulates through the body within the vasculature.
• In decreasing size order, vessels carrying blood away from the heart are, arteries, arterioles, capillary beds.
• In increasing size order, vessels carrying blood back towards the heart from the capillary beds are, venules, and veins
• The walls of most blood vessels consist of three layers called tunics.
• The innermost layer is called the tunica intima.
• Tunica intima consists of a thin layer of closely fitted endothelial cells.
• It is very smooth, to allow for smooth flow of blood
• The tunica media is the middle layer of tissue, and is primarily smooth muscle tissue and elastic connective tissue.
• This smooth muscle is controlled by the sympathetic nervous system, which changes the diameter of the blood vessels
• The tunica externa is the outer-most layer, and is mostly fibrous connective tissue that supports and protects the vessel.
• The walls of arteries are usually thicker than those  of the veins.
• Veins are subject to less pressure than ateries, but move blood against gravity.
• Veins contain one way valves to prevent backflow of blood