Proteins

 The basis of protein structure is the amino acid, of which 20 have been recognized as constituents of most proteins 

All Amino acids have amino group(NH2) and Carboxylic Group(COO2)

But, they are differentiated by the remainder of the molecule (R) as shown in the figure.

  

 

 Those amino acids that cannot be synthesized in the body and need to be taken from food are essential (indispensable) amino acids. 

Absence Essential amino acids from the diet leads to poor growth performance by a growing animal. 

Essential amino acids are labelled by (**) sign in the following table .

WHY DO WE NEED PROTEIN TO SURVIVE ?

We need protein for:

• Growth (especially important for children, teens, and pregnant women) 

• 10% - 35% of calories should come from protein.

• Tissue repair 

• Immune function 

• Energy when carbohydrate is not available 

• Preserving lean muscle mass 

• Synthesis of enzymes, hormones all antibodies

• Control Fluid movement in the body

• Buffer(PH control): Due to the carboxyl or acid group (-COO) and amino or basic group (- NH2)

Classification of proteins

Based on chemical composition.

 

1. Simple protein - yield amino-acids upon complete hydrolysis

           E.g.: - albumin - in eggs, zein of corn

2. Compound/conjugated proteins

           Protein + Non protein

           E.g.: - Hgb         (Protein + hem)  - Blood

II. Based on Nutritional Value:- This classification depends on the essential amino acids content of the protein.

1. Complete proteins: Contain all the essential amino acids in the proportion that is required to support growth and maintain tissues.

E.g. Almost all animal proteins except gelatine (lack two essential A.As.). 

They are denoted as complete because they resemble body protein (Egg & Milk).

    b. Incomplete Proteins: This refers to proteins that do not contain all essential amino acids in the proportion that is required to maintain growth and tissue repair

III.  Based on Conformation of the Protein: This refers to the three dimensional shape of the protein in its natural state. Based on this proteins are classified as:

1. Globular proteins

-Tightly folded poly peptide chain - spherical or globular shape

-Mostly soluble in water & salt solution

      E.g.:  - Enzymes, antibodies, and many hormones, Hgb

2. Fibrous proteins

-Polypeptide chains arranged in parallel manner along an axis

-Tough & insoluble in water 

E.g.:  - Collagen of tendons & bone matrix

-    Keratin of hair, skin, nails and 

-    Elastin of blood  vessels

IV.     Based on their Chemical Structure

1. Primary structure :    refers to the sequence of amino acids in the polypeptide chain of proteins held by peptide bond. 

Eg. Ala---gyc---Phenala---histd---tyr---trp

 

2. Secondary Structure: This refers to the folding of the polypeptide chain upon itself resulting in alpha helix (right twisted or left twisted) and or B-pleated sheet. This structure is held strong by intra molecular hydrogen bonding.

1.  Alpha helices                            OR

 

 

2. B-Pleated Sheath

 

 

c. Tertiary Structure: - This refers to the three dimensional arrangement of the protein structure (whether it is folded upon itself giving rise to globular proteins or whether its straight chain of poly peptides resulting in fibrous protein). This structure is maintained by the sulfide bond.

Biological Value of protein: If a protein contains all the indispensable amino acids it is said to have a high biological value.

 If a protein does not contain all the indispensable amino acids it is said to have a low biological value. 

High biological value (HBV) proteins include: meat, fish, eggs, cheese, and milk. 

Low biological value (LBV) proteins include: cereals, pulses, some nuts and vegetables. 

In general, animal protein sources have a higher biological value, than vegetable sources.

Nitrogen Balance

Definition: Nitrogen balance refers to the situation where nitrogen intake from food is equal to nitrogen excretion. 

This occurs in a healthy non-growing adult person taking adequate amount of energy from carbohydrates. 

In some situations Nitrogen excretion may be greater than nitrogen intake, this is called negative nitrogen balance. 

Other situations where nitrogen excretion is less than nitrogen intake from food are called positive nitrogen balance

Factors affecting nitrogen equilibrium

Positive nitrogen balance 

• Pregnancy 

• Lactation 

• Growth 

• Recovery from illness (Convalescent Stage)

Nitrogen intake = Nitrogen excretion (nitrogen balance)

Negative nitrogen balance 

• Starvation

• Devastating illness 

• Protein Energy Malnutrition 

Food sources of proteins

1. Animal source foods:-

• Beef, Lamb, pork 

• Fish, chicken  

• Poultry meat substitutes, cheese, milk, 

2. Plant source foods

• nuts, legumes, Soya bean cereals and legumes. 

Protein Requirements

• RDA average = .8 g/kg/day

• RDA athlete   = 1.2-1.6 g/kg/day

• High levels of protein intake above 2 g/kg/day can be harmful to the body 

 

Protein utilization

• Digestion

• Absorption

• Metabolism of protein 

MACRONUTRIENTS

 WHAT ARE MACRONUTRIENTS?

Macronutrients are nutrients that provide calories/energy. 

Since “macro” means large, they are nutrients needed in large amounts. 

There are three macronutrients:

• Carbohydrate 

• Protein 

• Fat 

Macronutrients contribute to the energy pool of the body.

While each of these macronutrients provides calories, the amount of calories that each one provides varies.

• Carbohydrate provides 4 K/calories per gram.

• Protein provides 4 K/calories per gram.

• Fat provides 9 K/calories per gram.

Besides carbohydrate, protein, and fat the only other substance that provides calories is alcohol.

Alcohol provides 7K/calories per gram. 

Alcohol, however, is not a macronutrient because we do not need it for survival.

WHY DO WE NEED CARBOHYDRATES TO SURVIVE?

We need carbohydrate because:

• 45% - 65% of calories should come from carbohydrate 

• Carbohydrates are the body’s main source of fuel. 

•  All of the tissues and cells in our body can use glucose for energy. 

• Carbohydrates are needed for the central nervous system, the kidneys, the brain, the muscles (including the heart) to function properly. 

•  Carbohydrates can be stored in the muscles and liver and later used for energy(glycogen). 

•  Carbohydrates are important in intestinal health and waste elimination (e.g.. Dietary fiber). 

Dietary fiber

• Fiber refers to certain types of carbohydrates that our body cannot digest (oligosaccharides and non-starch polysaccharides). 

• These carbohydrates pass through the intestinal tract intact and help to move waste out of the body. 

• Diets that are low in fiber have been shown to cause problems such as constipation and hemorrhoids and to increase the risk for certain types of cancers such as colon cancer. 

• Diets high in fiber; however, have been shown to decrease risks for heart disease, obesity, and they help lower cholesterol. 

• Foods high in fiber include fruits, vegetables, and whole grain products. 

Dietary Fiber prevents Constipation, Hemorrhoids & Diversticulosis by:

 

• Increasing perystalsis making stool bulk

• Decreasing intestinal transit time of contents

Food sources of Carbohydrates

• Free sugars are found from: fruits, juices, Soft drinks, milk, sugar, sugar cane, honey and yogurt, Cereal grains, Legumes & dried fruits, vegetables, processed foods (pasta), pastries, breads, candies , fruits like banana, dates, and sweet potato 

• Starch is found from: starchy foods (like cereals and legumes and potatoes), Other foods like fruits, vegetables, beans, nuts, seeds

 

• OligoSacharides are found from : Garlic, onion, Whole grain cereals and legumes

• Non starch polysaccharides are found from: Fruits, vegetables, Whole grain cereals and legumes

Carbohydrate digestion: Carbohydrates break down into glucose in order the body to absorb and use.

• Large starch molecules needs extensive breakdown. 

• Disaccharides - broken once

• Monosaccharide - don’t need to be broken down, 1-4 hours is needed for sugars and starches to be digested.

• Digetion of carbohydrate begins in mouth chewing releases saliva and enzyme amylase hydrolyzes starch to polysaccharides and maltose. 

• In the stomach no enzymes available to break down starch ,acid does some breakdown

• Small intestine -majority of carbohydrate digestion takes place here. Pancreatic amylase reduces carbohydrates to glucose chains or disaccharides and specific enzymes finish the job. 

• Maltase convertes maltose into 2 glucose, Sucrase changes sucrose into glucose and fructose and Lactase changes lactose into glucose and galactose.

• large intestine only fibers remain, attract water, which softens stool, bacteria ferment some fibers water, gas, short-chain fatty acids (used for energy)

Carbohydrate absorption: Glucose absorption can be started in the mouth where majority absorbed in small intestine. 

     Insulin 

•   The secretion is stimulated by Hyperglycemia and Parasympathetic nervous activity 

 

    Glucagon

• The secretion is stimulated by Hypoglycemia and Sympathetic nervous activity 

Requirements

• The RDA for carbohydrate is set at 130 g/day

 

• Minimum of 50 – 100 grams of carbohydrates/day are needed to avoid ketosis.

• Adults should consume 45–65 percent of their total calories from carbohydrates. 

Next Protein.... 

Urinary Tract Infections

 Urinary Tract Infections

Is an infection of the urinary tract and is subdivided into 2 general anatomic categories

Lower UTI – Cystitis and urethritis

Upper UTI – Perinephric and intrarenal abscess, acute pyelonephritis and prostatitis

Can be Acute or Chronic

Acute UTIs

Sub divided into Community acquired Acute UTIs and Nosocomial Acute UTIs

More common in women due to the short urethra

Etiology – E. coli most common cause.

Presentation is generally with urinary symptoms such as dysuria, frequency, urgency, hematuria and extra urinary symptoms like fever, lower abdominal pain, flank pain, nausea, vomiting, chills and rigors. May even have diarrhea

Diagnosis – Culture of urine gold standard but can also use urine analysis.

Urine culture – growth of >100,000 colony forming units of bacteria

Urine analysis – detection of WBCs (>5 in centrifuged, >10 in unspun specimen)

Supportive labs – Raised WBC in peripheral blood

Treatment

Remove risk factors – catheter, stones, etc

Treat the infection with antibiotics

Uncomplicated – Oral antibiotics – Amoxicillin, Norfloxacin, Ciprofloxacin, Cefalexin

Complicated – IV antibiotics – Ceftriaxone, Ciprofloxacin

Supportive management – antipyretics, anti-pain, anti-emetic, fluid resuscitation

Reference

Harrisons Textbook of Internal Medicine

Internal Medicine: Just the facts

Pocket Medicine, 4ed

Chronic Kidney Disease (CKD)

 

u Kidney damage or GFR <60ml/min/1.73m² for 3mo or longer.

o   Kidney damage is defined as pathologic abnormalities or markers of damage, including abnormalities in blood or urine tests or imaging studies.

·        Caused by either primary renal disease or secondary to a systemic disease

·        Risk factors for secondary causes include: DM, family history of CKD, Chronic use of NSAIDS, obesity and smoking

·        Screening is recommended for people with DM, Hypertension, family history of CKD using U/A, serum creatinine, etc

 

u AKI vs CKD - Features that support CKD include

·        Band keratopathy

·        Chronic anemia that is otherwise unexplained

·        Sustained increase in serum creatinine

·        Kidneys measuring <10cm in length on renal ultrasonography

·        Radiologic evidence of subperiosteal erosions consistent with advanced renal osteodystrophy

u Epidemiology

·        Growing public health problem worldwide

·        Significant racial and ethnic differences particularly at advanced ages. Africans and Hispanics have higher prevalence than whites

u Diagnosis

·        By GFR – MDRD, Cockroft-Gault formula

·        Cockroft-Gault formula

o       C_cr = (140-age) x body wt in Kg/(72xS_cr)

o       Multiply by 0.85 for females

u Management

·        Treat/Manage/control comorbidities – DM, Htn, Smoking, Obesity

·        Renal Replacement therapy – Dialysis

·        Renal transplant

 

u Complications

·        Electrolyte imbalances

·        Volume overload

·        Anemia

·        Encephalopathy

·        CVS those caused by AKI

·        Renal osteodystrophy