Urinary System

Consists of: Kidney(s) Ureters Urinary Bladder Urethra

Functions: Filter gallons of fluid from bloodstream – Filter plasma 60 times/day Responsible for removing: – Toxins – Metabolic Wastes – Excess ions Regulates volume and chemical make up of blood Maintains the proper pH between water, salts, acids and bases – Maintains blood pH between 7.35 – 7.45

Functions Regulatory functions include: – Produce hormones Renin and erthropoietin – Renin helps regulate BP and kidney function – Erthropoietin stimulates RBC production in bone marrow – Assists in metabolizing Vitamin D to its active form.

Kidney Anatomy Kidneys are covered by fatty tissue; anchors kidneys to posterior wall Internal Anatomy – 3 distinct regions – Pelvis – where kidneys join ureters; responsible for collecting urine – Renal Cortex – outer region; most of nephrons are found here – Medulla – Middle region; Renal pyramids Medulla

Nephron – Working Unit of Kidney; Carry out processes that form urine

Nephron Glomerulus – tuft of capillaries Parts of Nephron – Bowman’s capsule – Renal Tubule - 3 cm in length Proximal Convoluted tubule (PCT) Loop of Henle Distal Convoluted tubule (DCT) – Collecting Duct

Urine Formation Involves 3 processes Filtration  glomerulus and Bowman’s capsule Renal Reabsorption  Carried out by renal tubules Secretion  Carried out by renal tubules

Glomerular Filtration – Blood enters via afferent arteriole (larger diameter) and leaves via the efferent arteriole – Difference in vessel diameter increases BP in glomerulus and assists with filtration

Podocytes (Bowman’s capsule) – surround capillaries Passive, nonselective process where fluids and solutes are passed through a membrane Force is cause by hydrostatic pressure – What caused pressure increase?

GFR (Glomerular filtration rate) is the amount of filtrate produced in the kidneys in one minute. Renin regulates GFR by causing an increase in blood volume and blood pressure (Constricts blood vessels)

Filtration Pressure – Increase in BP at glomerulus forces water and solutes out of blood and into capsule. What passes through? What remains in the blood? Filtrate is not Urine

Filtrate contains both wastes and needed water and solutes Reabsorbion begins as soon as nutrients enters the PCT All water can’t be excreted, so tubules claim what it needs Why is it called reabsorption and not absorption?

What is reabsorbed? 100 % of organic nutrients Most electrolytes by facilitated diffusion Water is passively reabsorbed – 60 – 70 % of fluid is reaborbed by PCT Rate and degree of reabsorption is regulated by hormones Problems: Hyperglycemia

Where does Reabsorption occur in the nephron ? PCT are most active reabsorbers The descending loop of Henle is permeable to water but not solutes The ascending loop of Henle is impermeable to water and most solutes – Na and Cl are actively reabsorbed into the blood stream DCT is impermeable to solutes Reabsorption of Na, K, and water is controlled by hormones

Figure 25.18a Cortex Outer medulla Inner medulla (a) (b) (c) (e) (d) Na + (65%) Glucose Amino acids H 2 O (65%) and many ions (e.g. Cl – and K + ) 300 Milliosmols Blood pH regulation H +, NH 4 + HCO 3 – Some drugs Active transport (primary or secondary) Passive transport (a) Proximal convoluted tubule: 65% of filtrate volume reabsorbed Na +, glucose, amino acids, and other nutrients actively transported; H 2 O and many ions follow passively H + and NH 4 + secretion and HCO 3 – reabsorption to maintain blood pH Some drugs are secreted

Reabsorption (b) The descending loop of Henle Freely permeable to H 2 O Not permeable to NaCl or other solutes Filtrate becomes increasingly concentrated as H 2 0 leaves by ____________? Active transport (primary or secondary) Passive transport

Figure 25.18c Na + Urea Cl – Na + Cl – K+K+ (c) Ascending limb of loop of Henle Impermeable to H 2 O Permeable to NaCl Filtrate becomes increasingly dilute as salt is reabsorbed (a) (b) (c) (e) (d) Cortex Outer medulla Inner medulla 300 Milliosmols Active transport (primary or secondary) Passive transport

Figure 25.16a Loop of Henle Osmolality of interstitial fluid (mOsm) Inner medulla Outer medulla Cortex Active transport Passive transport Water impermeable The ascending limb: Impermeable to H 2 O Permeable to NaCl Filtrate becomes increasingly dilute as NaCl leaves, eventually becoming hypo-osmotic to blood. NaCl leaving the ascending limb increases the osmolality of blood. Filtrate entering the loop of Henle is contains many substances that are needed in the body The descending limb: Permeable to H 2 O Impermeable to NaCl As filtrate flows, it becomes increasingly concentrated as H 2 O leaves the tubule by osmosis. The filtrate osmolality increases. H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O NaCI

What’s left in the nephron? Non-reabsorbed substances are: – Urea – Urea – 50 % is reclaimed; the rest is waste – Creatinine – Creatinine – a large lipid; insoluble molecule that is not reabsorbed at all – Uric Acid – Uric Acid – 50 % is reclaimed; waste product of RNA synthesis

Tubular Secretion – “Reabsorption in Reverse” Urine is formed from filtered and secreted substances Secretion occurs in the DCT tubules and collecting ducts – Hormones assist with this process ADH (antidiuretic hormone) Aldosterone ANP

Figure 25.18d Na + ; aldosterone-regulated Ca 2+ ; PTH-regulated Cl – ; follows Na + (d) Distal convoluted tubule Na + reabsorption regulated by aldosterone Ca 2+ reabsortion regulated by parathyroid hormone (PTH) Cl – cotransported with Na + (a) (b) (c) (e) (d) Cortex Outer medulla Inner medulla 300 Milliosmols Active transport (primary or secondary) Passive transport

Figure 25.18e Blood pH regulation Urea; increased by ADH Na + K+K+ H+H+ HCO 3 – NH 4 + H 2 O regulated by ADH Regulated by aldosterone: (e) Collecting duct H 2 O reabsorption regulated by ADH Na + reabsorption and K + secretion regulated by aldosterone H + and HCO 3 – reabsorption or secretion to maintain blood pH Why? Urea reabsorption increased by ADH Why? (a) (b) (c) (e) (d) Cortex Outer medulla Inner medulla 300 Milliosmols Active transport (primary or secondary) Passive transport

Substances that are not reabsorbed Substances that lack carry proteins along membrane – Urea – Uric acid Substances that are not lipid soluble Substances that are too large to pass – Creatinine

Label the parts of the nephron Describe what is occurring at sections

Hormonal Control of Secretion Osmolarity – number of solute particles dissolved in one liter of water Affects osmosis Kidneys are responsible for regulating solute concentrations in the body; the concentration of urine is regulated by hormones Four Hormones Control Kidney Function – Renin – Aldosterone – Atrial Natiuretic Peptide (ANP) – Antidiuretic hormone (ADH)

Renin Released when glomerular pressure is low Causes blood vessels to constrict; raising blood pressure in arteries The efferent arteriole constricts which increases glomerular pressure Stimulates secretion of ADH and aldosterone

Aldosterone Released by adrenal glands When secreted causes Na + to be reabsorbed from DCT H 2 0 follow Na +, so both Na + and H 2 O are reabsorbed Eliminates K + into urine Stimuli that cause the release of aldosterone – Decreased blood volume – Decreased sodium in blood – Increased potassium in blood (heart block)

If too much aldosterone is secreted: - Excessive Na + and H 2 0 retention (edema, hypertension - Accelerated secretion of K ions (muscle responsiveness)

Lasix – (Diuretic) inhibits Na from being reabsorbed; thus water is not reabsorbed.

Atrial Natiuretic Peptide (ANP) Works against aldosterone Released by atrial cardiac cells when blood volume and BP are too high. Why would the atrial cells detect a change in blood volume? When ANP is secreted: Na + – Causes Na + to be dumped into tubules (urine) – H 2 O – H 2 O follows sodium into urine – Capillaries in glomerulus dilate; increasing blood flow to Bowman’s capsule; increasing UO – Inhibits the secretion of renin, aldosterone and ADH Na + H 2 O – Urine contains more Na + H 2 O; blood pressure and blood volume decrease

ADH (Antiduretic hormone) When ADH is secreted, water is reabsorbed from DCT and collecting tubules Person feels thirsty When ADH is not secreted, DCT and collecting tubules are impermeable to water, no reabsorption occurs here.

Urine Concentration of Urine is controlled by ADH Dilute Urine Dilute Urine – Na and other ions are removed from filtrate – Urine appears clear in color Concentrated Urine Concentrated Urine – ADH is secreted; distal and collecting tubules reabsorb water – When water leaves filtrate; urine concentration increases

Work of the Nephron with Hormone Secretion

UO Diuretics – chemicals which increase UO Any substance that is not reabsorbed and carrries water out of body – Alcohol – inhibits ADH – Caffeine – Increases filtration rate (GFR) Diuretic drugs are taken for CHF, edema and to increase UO

Figure 25.17a Active transport Passive transport (a) Absence of ADH Large volume of dilute urine Collecting duct Cortex NaCI Urea Outer medulla Inner medulla DCT H2OH2O H2OH2O Descending limb of loop of Henle

Maintaining a Balance Other Systems assist in excretion and affect kidney function – Integumentary – Respiratory – Digestive Fluid and Electrolyte Balance – Water into body = Water out of the body – Neither a net gain or loss of electrolytes should occur in body Acid-Base Balance – Blood pH ranges between 7.35 – 7.45 – Kidneys will secrete H + ions when blood pH drops

Acidosis – Blood pH drops below 7.35 – Respiratory Acidosis Due to an increase of CO 2 levels in body – Metabolic Acidosis Due to cell metabolism in the body Lactic acid in muscle metabolism Ketone bodies by the breakdown of fat Diabetics don’t use glucose due to lack of insulin; so cells will break down fat instead Blood ph < 7.05 disrupts the stability of cell membrane, alters protein function (enzyme), causes heart arrhythmias and leads to coma

Kidney Stones Hardened mineral deposits that form in kidney Symptoms – Blood in urine – Increased need to go – Nausea and vomiting – Pain during urination – Tenderness in abdomen and kidney region Treatment – Lithotripsy – Medication

Renal Failure – Kidney Failure Nephrons in kidney stop functioning – Unable to filter or excrete waste – Can’t regulate composition of body fluids – Can’t control erythrocyte function or blood pressure – Can’t control salt balance